Thank you everyone so much for your advice! I really appreciate it. This has helped me solidify my resolve on this issue and finally confront my girlfriend directly last night.

It turns out that, as has been mentioned before, she doesn't "need" her dog in her bed, she just "wants" her in the bed. She did readily admit this and added that she's slept with pets in her bed since she was a very young child, so it's not a BP thing so much as a comforting habit. She called it her "security blanket."

When I first presented my argument and all the research I've been doing on the health risks and my own personal concerns, she said that it would be hard for her, but she was relatively relieved since she was convinced I'd be a total asshole at some point and demand that she get rid of her dog. She asked me what I would do if instead of getting more tolerant of the dog dander, I became worse, and I said that I'd go in for the immunotherapy. This, I think, touched her a lot, because she would have been willing to get rid of her dog if I'd demanded it. That in turn touched me, and it was all sweet for a couple minutes. XD

She says she needs to do some thinking on it and get used to the idea, but that my health is more important to her and that she wants our relationship to be about taking care of ourselves and each other. This is the epitome of what I wanted her to say, so I was very relieved, even though she's still having trouble with the idea and is wanting to "meet me hafway" by having the dog on the bed, but not under the covers. I'm convincing her that this is beyond halfway for me, since I'm agreeing to live with a dog that I'm allergic to.

Still, it's a good start, I think, and I'm glad I came to you guys with the problem. Usually I'm horrible at communication and bringing up things that are bothering me, so this was rough.

Anyway, I do have another question:

We're very poor college kids, so we're moving into a studio. During the day when we're both in school, the dog is likely to jump up onto the bed anyway, which will not be too bad since her dander will already be on the couch, the chairs, my clothes, etc, so it'll all be bad no matter how you look at it. I'm just wondering if you have suggestions or advice for maybe keeping the dog off the bed while we're not there since there's no door to block her off, just to try and make it as dander-free as possible.

Or am I going to have to spray down/wash my comforter and pillow cases religiously?

The reason I freak out so much about dander in my sleeping space is because I'm breathing it in a concentrated amount as I sleep, which apparently makes it much more likely that I'll have a bad allergic reaction, which at the very least will disrupt my sleep unnecessarily.

Thanks again.