Sister carrying my child?

My sister who is 18 and I were talking the other day. We believe I am unable to have children. Her and I were just talking about my infertility and she started telling me how she has considered being a surrogate for my husband and I. She said it would be weird, but at least her sister would have a child. This really touched my heart, and my husband and I have actually thought about asking her to do it for us. We would wait till she is a little older because she is still really young. Do you think this is too much to ask of her? She is in college right now and I don’t want to interfere with her life too much, but we do desperately want a child. Any advice or thoughts are appreciated.