I feel like I should offer some insight of my own. To set the scene, I am 23 now and I first moved out of my mom's house before I graduated highschool(I think I had just turned 18 and I technically graduated early. I had no classes and didn't need to attend for the second semester but I still had to do the "senior stuff" and go back to complete my senior project and walk). I have lived with A LOT of people. The only time it has ever worked out was when I was living with very good friends like I am now. We tried doing the craigslist, rent a room thing and the first time we ended up getting attacked in the middle of the night by the man we lived with. Had to call 911, involve a lot of police and attend court for that one. It also left us homeless for about 8 months during which time we lived in my brothers shed. Now, it's not what most think of when they think of a shed, it's big, about the size of a large garage, had a woodstove and electricity and it also served as his studio for his band and fellow musicians to play and party. There was no running water or bathroom and even with the woodstove it got very cold in the winter. There were also many nights where the guys were up partying until 2-3am, BUT it allowed us to keep our dog whom we've had since he was 5 weeks old. We actually had quite a few places we could stay but not with the dog so we opted for "the shack". After 8 months of that we couldn't take it anymore, we were spending so much money trying to keep our food cold, we didn't have a fridge so we used a cooler, trying to buy dishes and things that didn't need washed, etc. It was like camping for 8 months straight and it was expensive, and we were paying him "rent" on top of it. We ended up having no other options and tried the craigslist route again. We moved into the middle of the city with a lesbian couple that seemed nice enough when we met them. After we moved in we realized that they were the biggest slobs and were always either violently fighting or having sex and honestly, I'm not sure which was louder. They were also constantly borrowing money that we would never get back and raising our rent for one reason or another. When we moved in they said the dog was okay, but then the landlord decided it wasn't since another family moved in downstairs and didn't like that we had a dog, we were left with 3 days to move out. Luckily my friend came to the rescue, we stayed with her for awhile and finally got the place we live now and we absolutely love it. It's not the cheapest but it's a huge house with a pond, greenhouse and 4.5 acres of land and woods that are "ours" and about another 5 acres that we are allowed to use. It is my boyfriend and I and two good friends. We all get along great and it's working out very well. But we did just have someone move out this week. It was a long time friend of mine that bugged and bugged to move in, we finally said okay and he caused problems from day one and ultimately, him living here has completely ruined our 8 year friendship and we're all just glad to have him out.
Sorry for the long story there but I guess what I'm trying to say is, if she is causing all of these problems and you don't even live together yet, I really think you are going to save yourself a big headache by not signing that lease with her. She may be older than you but it seems like she has no idea what it really costs to live on your own. She has no car, no license, and if she thinks $200 is enough to live in a 2 bedroom duplex, she is insane. Wait until she realizes how much groceries, gas(I assume she will need to get rides to places), clothes, etc cost. Add a dog on top of that and you have dog food, flea/tick medicine, annual vaccinations, heartworm tests and meds, neuter, toys, leashes, any thing that just comes up like sickness, injury, etc. And for the record, I don't know of any rescues or shelters that will adopt out to a person that plans to keep the dog outside 24/7.
We're only going to be roommates because we're best friends and she's still loving at home at the age of 23 (soon to be 24) with out a car or license. She just thinks that I'm going to do everything to find the place when I live about 100 miles away. There's only so much I can do online. I asked her to get her license before I move back and she still hasn't taken the test for her permit and she isn't helping me look for a house. 
