If your neighbor is trustworthy I would definitely go with her! First of all if she is only caring for one other child then your little girl will get a lot more attention and one-on-one care. In daycare centers the teacher to child ratio usually runs about 4-5 infants to 1 teacher. Second, in a daycare there is more of a chance of your child getting sick as opposed to sending her to your neighbor's house. However, if you send her to your neighbor I would be sure that your neighbor does activities that allow your little girl to learn developmental skills. In a daycare (if it is a good one) they will most likely require the teachers to have a daily or weekly lesson plan to promote the development of skills in the children.
Daycare centers can be good too. I actually work at a daycare and we have very strict guidelines we have to follow. Unfortunately I can't afford for my girls to go to the daycare I work at so they go to a different daycare. I'm not happy with the situation but I have no other option right now.
I will warn you that your child will get hurt at some point in time whether it be at a daycare, your neighbor's house, or in your own home. Accidents always happen when you least expect it. My 4 month old got her first scratch at daycare last week. It breaks my heart that it happened, but as a teacher and mother I know that things happen. Her teacher had a child on the changing table changing their diaper and wasn't able to get to Eden before the other child scratched her. My 2 year old has had her fair share of injuries as well.
Good luck with whatever you decide to do. If you have any more questions about daycare or anything I would be more than happy to answer them! :)