Present for my sister

I am having a hard time coming up with a present for my sister. She had her daughter a year ago, and has nursed her for the last 10 months, and has had some supply issues, stuff like that. Nursing hasnt always been real easy for her. Now she is continueing to pump for my son now that her daughter isnt nursing anymore. I am soooo thrilled that she is doing this for me. I only produce like 3 ounces a day at the most.(since ive gone back to work, my supply suxs!) Anyways, she offered to continue to pump for me even before we were matched. Now my son is 3 months old and she is providing me with almost 3/4 of the milk he needs for the day. I am only using like 6 or 8 ounces of formula a day. She says she doesnt want anything for doing it. Shes just happy to help out and knows that breastmilk is the best for my baby. I really want to get her something so that she knows how much i appreciate her doing this. She so committed to have already nursed your own child and now have to pump 5 or 6 times a day to give to someone else for their child. She assures me that she is just happy to help me and that is payment enough. Any thoughts on what i can get her?? I want it to be special, but am drawing a blank. I know they dont have a whole lotta extra disposable income as she works part time and her DH is in College full time. but i think money isnt exactly the way to show my appreciation. I dont know how long shes going to pump yet, but i want to have an idea ready so when she's done I can give it to her. Its just such an amazing thing to me that she doesnt even think twice about doing this for me. Espiecally since its such a pain in the A** to pump sometimes when she's busy with a job and 2 kids. Im so thankful to her and i want to show her that appreciation. Any suggestions?? Thanks,Rach