S.L.
This is a long reply, so I'm sorry about the book, but I think there are a lot of issues going on...
There are many reasons to keep nursing a toddler. www.kellymom.com is a great resource to research those, as is the book "How Weaning Happens," which has wonderful information about why you would nurse a toddler, as well as some great ideas for how to wean when you are ready. That being said, it doesn't sound to me like your sister is in any hurry to wean. It just sounds like Mom is at the end of her rope, and weaning seems like it will make the problem go away. Unfortunately, that isn't true. If you have a strong-willed child who is throwing a tantrum at the breast, she's just going to throw her tantrums about something else once she's weaned. I say this from experience!
The heart of the issue seems to be boundaries. It sounds like your sister feels like her daughter won’t respect her boundaries, and she is tired of it. Nursing manners are nothing more than boundaries, which parents should be setting for all toddlers. If the biggest issue is waiting for nursing, then there are a couple things to consider. First, some compassion is definitely called for. It is hard for little ones to wait. That doesn’t mean that they can’t or shouldn’t learn, but it does mean that we can show them some sympathy and remind ourselves as parents when we are frustrated that this is hard for the kids, too. Second, it will probably help if you niece has something of a schedule to her nursing. A routine helps her know what to expect. Without one, your niece can’t understand why Mommy says yes this time and no another time. Mom doesn't have to schedule by the clock, but some kind of routine is helpful. When my girls were that age, we nursed first thing in the morning, and before naps and bedtime. Beyond that, I would nurse them when they were hurt. Other than that, if they asked out of the blue, they were told that they had to wait until whenever then next nursing time was. If your sister is uncomfortable nursing in public, or unwilling to interrupt errands to nurse, it can help to set a particular spot in the house as your nursing spot. Then she can easily say, "We only nurse in the rocking chair. Once we get home, Mommy has to put the food in the fridge and then we'll go nurse in the rocking chair." I did this with my girls, and it was so easy because it was so concrete for them - no rocking chair (or couch, or special pillow, or whatever), no nursing. Finally, it is important to follow through. I’m totally guilty of this - I tell my girls “just a minute,” then ten minutes later, I’m still on the phone, reading my book, or doing whatever. Your sister should give her daughter a concrete time, then follow through. Instead of saying "Mommy needs to finish up on the computer," or something that is so vague that her daughter doesn't know what to expect, set a concrete time - timers are great for this! Say something like, "Mommy needs to answer this email. I will nurse you in two minutes when the timer goes off. Listen for the timer to go 'DING,' and then we will nurse." Then she can set a kitchen timer, stop what she is doing when the timer goes off, and nurse as promised. When your niece learns that Mommy will do what she says, when she says it, she will learn to wait and to trust Mommy to follow through.
Once she sets reasonable boundaries, your sister has to be willing to enforce them. She's not going to get around the problem by weaning her daughter. She'll still have to set boundaries over jumping on the couch, running into the street, or having chocolate for breakfast. With a strong-willed child, she will have to reinforce her boundaries over and over again. There will be times when she will be in a power struggle with her daughter and times when her daughter will throw tantrums. It's just the nature of parenting. Tantrums over nursing should be dealt with the same way she deals with any other tantrums. When my girls throw tantrums (in relation to anything, not just nursing), I tell them something like "It hurts Mommy's ears when you scream like that. I'm going to put you in your room so you don't hurt my ears. You can come out when you are all done crying." If your sister doesn't want to send her daughter to her room, she can just walk away. Some moms like to sit quietly next to their child until their child is done. That always wound my kids up more when they had an audience. If your sister is willing to nurse her daughter, but not willing to give into a tantrum, she can say something like “Your crying hurts Mommy’s ears. I can’t make milk when my ears are hurting. When you are all done crying, I will sit on the couch with you and nurse.” Unlike a previous poster, I would NOT recommend laughing at the child or telling them they are being silly. Obviously, they don't feel like whatever they are crying over is a silly issue, and that is such a disrespectful thing to say to someone who is upset. We would never respond to a crying friend like that! You can empathize with the feelings without allowing the bad behavior. One thing that helped head off tantrums for my girls was teaching them to name their feelings. I would say something like "You are FRUSTRATED right now, because you can't nurse. It's hard when Mommy says no. I understand. When I don't get what I want, I feel frustrated too." Then you give them an acceptable way to express their feelings. "You can tell Mommy, I feel FRUSTRATED. You can also hit a pillow if you feel frustrated. You cannot scream at me. If you need to scream, you can scream in your room." I felt pretty silly doing this with a 12 months old, but they eventually got what I was saying, and it helped! I’ll never forget my oldest, at 18 months, telling me through her tears, “I feel FWUSTWATED! I just need to go in my room and cry right now.” Then she took herself off to the nursery, cried for a while, then came out and went about her business.
I agree with other posters that have pointed out that your niece is obviously not ready to wean. While this doesn't mean your sister can't wean her, it does mean that it's going to be more difficult if that is what she decides to do. It’s not likely that if she just goes away for the weekend, your niece is going to lose interest. I have weaned one daughter who was ready, and one who was not. With my first, I went slowly down to one feeding a day, then left for the weekend. It was so easy, and I thought I had the perfect answer. Then I weaned my second daughter, who was *not* ready, and it was a nightmare. Six months later, she still bugs me about nursing. She still reminds me that my milk is going to come back when the baby is born, and I just know that she is going to ask to nurse once her baby sister is born! I realize that it wasn't the method that made it easy, it was the fact that my oldest was ready, while my second was not.
My best advice for your sister would be to find a local La Leche League meeting. She can look them up on the La Leche League, Intl. website at http://www.llli.org/WebUS.html. There she will meet other women, including moms who are nursing toddlers. We’ve all run into the same issues. It is so priceless to be able to talk it out with other moms who have been there. Sometimes the only answer she’ll get is “We’ve been there, too. This too shall pass.” Sometimes she’ll hear “Trust your gut. You know what’s best for you and your baby.” Sometimes she’ll get some really great advice that makes all the difference in the world. Whatever she hears, that kind of community is invaluable. I know there is a LOT of information in this post. I hope your sister finds something that helps her and her daughter.
Best of luck,
S. L