I'm sorry to say this, but it really doesn't sound like you should get married to me, mostly just from the tone of your post. You're not at all excited about it and have some sort of pit in your stomach about it telling you it's not right. I would pay attention to those feelings. It's normal for guys to be very cautious about getting married, but the feelings you're having are not normal for someone who truly loves a woman and wants to be with her the rest of his life (or the next 10-15 years to start a family at the very least). Seven years should be plenty long enough for you to know if it's right. It doesn't sound like it's right.
I do think it is good your girl has been better these last two years, but I would fully expect the worst days would still be ahead of you, especially if you get married. This might sound misogynistic, but women usually (or at least often) show their worst selves after getting married. It might not happen right away, but at some point it will. Ask yourself if you could handle reliving the worst times of your relationship again. If that makes you squeamish, then that's a pretty good indicator you should not go that route.
I'm just some guy on the internet giving you advice based on the limited info you provided though, so take my thoughts with a grain of salt. I think you're completely wrong in saying it's "not fair" to her. That's not even a thought you should have. You need to do what's right for you.