I think that you are worrying too much about this - it is perfectly normal for a child to react to the birth of a new sibling with behavior such as this, and it is actually still very common for children as old as 3 1/2 to still regularly use their pacifiers for comfort at naptime and nighttime. She is indeed doing this for attention - but instead of being upset or angry that she is reverting in this way, consider what a huge transition it is for her when you brought this new child into "her" home without even asking her permission! She has been an only child for 2 1/2 years now, and almost over night, she is no longer mommy and daddys one and only - and while I am sure you and your husband are making time to give extra attention and love to your little girl, her place has still been totally usurped in her own home.
You need to give her time to adjust, and she may need more time than you would like to give her - but pushing her to get rid of the pacifier or making a big deal out of it when she does hijack your sons binkies will only cause the behavior to be stronger, and to continue for a much longer period of time. She is old enough now to understand compromise, so this is what I suggest:
delegate a binky for her to use when she feels like she needs it (so she doesnt steal her brothers pacifiers) - she can use it in the house, but it is not allowed to take it out in public, have it at the dinner table, or whatever rules you want to attach to its use. When her limited use of the pacifier is no longer a criminal act, it will loose its appeal, and she'll soon give it up when she is feeling more comfortable with the situation at home. And if you feel like her use of the binky is going on for too long (like, shes still continuing to want it regularly for a period of longer than a month or two), cut the tip of the nipple off of her pacifier. She will pop it in her mouth, but it will no longer hold its appeal - however you will have to keep your sons pacifiers out of sight and mind apart from the one he currently has in his mouth so that she is not tempted to horde them!
All in all, the more you ignore the behavior and give it credence, the sooner it will go away. Its normal, healthy, and expected of a toddler her age.