A.S.
The benefit to a child past 12 months is mostly the same as it is prior to that. It is easy to digest....so if they are sick alot of times it is the only thing they will eat. You pass on the antibodies your body makes in your milk. So, if you baby gets sick and you are in close contact, your body starts to make antibodies (assuming you have been exposed to that before) which are passed to your baby through your milk, regardless of the age. Your milk also gets more "potent" persay, as the child gets older, so even though they get less, the milk that they do get is packed with antibodies and dense in nutrition.
Really the only difference is that prior to 12 months, the brain cells are rapidly forming and the fat in breastmilk is important in this formation.
There is a lot more information here. http://www.kellymom.com/bf/bfextended/ebf-benefits.html
http://www.kellymom.com/bf/bfextended/ebf-links.html
I found nursing a toddler to be much more beneficial to me personally too than nursing a baby. The bonding time is very important and powerful. A toddler is so full of energy and running running running all the time. This is abotu the only thing you can get them to stop and chill out for. It is less invconvienient as they get older because you do it less often and they understand the concept of "later" so if you are busy you don't have to stop right away and nurse. The hormones released when nursing helped me to calm and center myself everyday after work, and help remind you of what is really important in your life and that that child is all that matters.
I am curious why you are supplementing your daughter? It is really in her best interests to get only breastmilk. Any other food before 12 months removes some of the healthy intenstinal flora. http://breastfeed.com/resources/articles/virgingut.htm
Some mothers have to supplement, but if your child has been small all along it is much more likely just her genetics than any issue with how much she is eating. If you visit an LC they can weigh your child before and after she nurses to see how much she has gotten to eat. As long as she stays in the same area percentage wise, give or take a little, she doesn't need any formula, and actually you are lucky that she didn't have any issues with nipple confusion, starting very young with bottles (my son did).
I went back to work full time at 10 weeks and pumped for my son till he was 14 months. Then I continued to nurse him only when I was home until he was 29 months and self-weaned. It was the hardest, but most worthwhile experience I have ever had in my life. We struggled ALOT, but in the end, I am sooo glad I stuck with it and made it work. My child is healthier because of it, and we have a fantastic relationship. He is extremely well adjusted and I like to think that our nursing relationship had alot to do with that.
Congratulations on your little girl and much luck to come!! Feel free to contact me anytime if you need anything. I am hoping to become an LC someday and have just started studying for it.
also......Experts don't reccommend 12 months as the time to wean. What they do reccomend is exclusive nursing (no other foods) to at least 6 months, and to continue nursing till AT LEAST 12 months. 12 months is not any kind of magic age where they start getting less out of breastmilk, it is only the time when their digestive system is more mature and more able to handle to potential allergens in cow's milk. 12 months should be considered the earliest to introduce other kinds of milk rather than a time to wean. Each child has their own time table as far as this goes.