Sister pregnant asking us to adopt????

My 18 year old sister is pregnant. This sounds silly, but she's the baby of the family, and is in every way possible. She can't even make herself a peanut butter and jelly sandwich. She dropped out of school and has unresolved anxiety issues. My husband and I are 27, he has a career and I am finishing my degree in social work. We are newlyweds, with no children, and living together AFTER marriage, it is our first time out of our family homes. We make it work although it's tight, we have everything we want and need. We are not TRYING for a child, but we follow my ovulation and just go on that, therefore if it were to happen it's really not a surprise.

Anyway, my sister decided to ask us to adopt her child. I personally am against abortion, I have gone through it at 15 and I would never wish it on anyone, I just don't know what the best answer is for this. It's a huge step, and as I said my husband and I have no children. We would never want to see it go into the system and wouldn't let that happen, but we see a sticky situation if we were to adopt it and really don't know how to decide or where to turn. Any helpful advice, tips, people who have been there etc? Thank you so much!