This is purely from a woman's perspective...and I'm trying to remember what I was like when I was 18...
When I was 18, I always looked up to older men. I had a thing with older men - something about the age and authority figure. Yes, you're only 25, but to an 18 year old GIRL that is a MATURE MAN. Not only did I like older men, but I had a tendency to fall for them. Especially if they were good 'friends' and they seemed to take care of me.
I'm not saying things would go BAD, but I would say if you rent the room to her, be very very cautious. Neither one of you would plan on something 'more than friends' coming up, but 18 year-old girls don't usually intend to fall for their guy friends either. She's at a very vulnerable age. She's probably excited about adulthood, all the benefits/responsibilities it brings, and just learning to understand the sexual control she could have over a man. (I was a total flirt when I was 18, but I didn't quite know how to control it after the flirting took a further step.) I have a feeling she'll fall for you, even if there's no attraction to begin with. Women have a tendency to fall in love physically after other attractions are established. To her you may look mature, responsible, and available (in many senses of the word) - and become very attractive to her.
Personally, I don't think it's a good idea that she move in with you. But I don't know you or her either. Every situation is different. But I guess this is just my two cents. I hope it's helped!
Billygoat
PS: What congregation in Wichita were you in? I was from Lynwood on the south side of town.