If you feel she is getting all the nutrition she needs then she is using you as a human pacifier. It sounds like she just likes to suck in her sleep. I would disengage her after a normal feeding time and gently lay her in her own bassinet or crib. We never co-slept. Mine always slept beside me in a bassinet. I was always scared my Double FF boobs would smother the baby when I was asleep or that I would roll over on him and hurt him. IF it is truly an issue of hunger than I would supplement her with a bottle at night to help her sleep and the nutrients last. You can always pump and offer her breast milk in a bottle. My third child wanted to be on the breast all the time. He woke every 45minutes and then nursed for 45 minutes or longer. But when he slept it was only for 45minutes until he wanted on again. All night long. I knew my breast milk was fine, when mine seperated out it was always with a thick layer of fat at the top an inch or more thick with all 3 babies. So I knew it wasn't that. But he was also 9 pounds when he was born. He just needed a lot of nutrition.
The other thing you might try to do is let her cry a little longer, then lengthen the time between crying bursts. To get her used to not being on the breast at night 100% of the time. At this age it isn't necessarily being spoiled as in setting up some bad habits for her to learn to comfort herself. She is comforting herself with you is what it sounds like to me.
But everyone has to do what they feel is right. To some solving this problem is to co-sleep and she will outgrow it. I just took a different approach for what worked for us. I always figured if we co-slept then later I would have another habit to break, of them needing to learn to sleep in their own bed after sleeping with mom and dad for a year or two. Same thing with a paci. Never started one, because I would just have to break that habit eventually also. But don't mistake, I did let mine have their mama-paci just not for 5 hours straight. They do need to be with you alot at this stage, for comfort and warmth etc. But they also will begin to develop some bad habits and as parents we usually let them, and then it comes back to bite us in the butt later.
The added bonus of having her get a bottle for at least one feeding is that dad can give her a feeding also and get up and maybe let you get a little more sleep. Maybe he could start by giving her a bottle at bedtime and then letting her wake-up later for you to nurse. Pretty much anyway you go there is going to be some crying while helping her get into a new routine. But you will be so much better later when she is older. It will be easier as a 15 month or toddler that she had a good routine. Not a routine in stone, but the things that you do to prepare her for sleep. Some rock, some bathe them, some play music. Whatever you start out doing is what she will learn is the "routine" and any deviations from that will be hard for her to cope with. And it gets worse the longer they go with a set routine and the older you get.
I am a member of a mom's group on yahoo groups. Creative parenting. You can sign up. We have a mom that is a La Leche League consultant. You can ask her anything. Her name is Robin. But I am also sure that your local hospital has a lactation consultant, call back to the hospital where she was delivered and see if they have someone to help you. She is young enough that you guys should qualify for them to continue to give you supportive help, I would think.
Anyways, I have given you all my ideas.
Good luck,
L.