Wow, so much feedback. Thank you guys.

Some points of clarification:
1) Yes, I meant 2 parking spaces. Typed that wrong.
2) This coworker is actually a good friend to both of us. She's also currently in a relationship. Her boyfriend has to temporarily work out of state. This is why she would stay for 3-5 months, because depending on when her boyfriend returns that's when she would look for a new place with her boyfriend. Dual income makes it more possible for her to rent a different place.
3) No, my boyfriend doesn't see her as a romantic interest. It's very clear she's not his type (different ethnicity), she's in a relationship, and he's not looking elsewhere for a serious relationship. I have no qualms about this.
4) I realize I listed a lot of cons. Some pro's for her moving in would be that she's someone who has experience with graduate school. My SO is starting grad school this fall and he's not sure about how he will handle the immense amount of stress that comes with juggling full-time work and studying. She could offer valuable insights and also keep me company on nights when he has class late until 9 PM.
5) I don't think lending her money would be the answer. That might actually make her feel guilty borrowing our money. She's the type of person who would rather it be in some form of an exchange (even if it's a bargain deal).
6) My SO is also going to be taking on student loans for graduate school. So needless to say, he could use some extra income here and there. She knows that his tuition is not cheap, so that's another reason she'd be less inclined to borrow money from us.
7) I do worry it would be hard to ask her to move out if it becomes longer than 5 months. There would be no easy way to handle that since she's a good friend to us.

I think overall, I already know how I feel. It looks like you guys agree that I shouldn't go through with this arrangement. There may be other ways to help her, just not at the cost of building my own relationship. We usually just pick up the bill when we go out to eat as a group. Small things.