Often I feel like she doesn't want it to work.

Not being open to changing herself so that she thinks a little before saying something that "just needs to be said", is a pretty solid indication that she isn't thinking about you or how you will feel once she has said her piece.

I'm an ENFP, and honestly, I say stuff without thinking because it is on my mind, and saying it makes me feel better. I spend a lot of time with an INTJ, and have been asked to think about what I say, and whether it actually needs to be said. I guess I am a glass half full because I have dealt with depression for years. I'm working on the word vomit, because it will benefit a lot of areas of my life.

You should sit down and explain this situation and your worries to your SO. I'm pretty sure that is what you do in a serious relationship, and if she doesn't want to sit there and at least listen to your concerns, then I don't think she really wants it to work.

"It's not going to last anyway but I'm going to enjoy the time we have."

I also see thing like this and have recently realised that by thinking this way, you can perpetuate your own unhappiness. When you think something isn't going to last, you see no point in putting in the effort to make it work, to make it better, or to purposely do thing you enjoy. Not beneficial for a relationship at all, and I would guess you guys will break up if she doesn't change.

INTJ's aren't perfect, but OP you seem like a nicely developed INTJ, aware of their flaws and happy to change them. That's a thumbs up in my book. If your SO won't take what is troubling you seriously, even more so when she is the source of that, then I don't think she is ready for a relationship.

When it comes down to it, if you love someone, sometimes you have to do what is best for them, even if it is not what is best for you. You do what makes them happy, you do what boosts their confidence, because every relationship has a compromise, and if one party doesn't know when to not be stubborn, then it usually just leads to excessive conflict.