My gf and her budget, why does she get upset?

maybe she doesn't take criticism well, or maybe she doesn't want to seem incapable in any way to you, or maybe she doesn't want to be told what to do.....is she stubborn and prideful? if so, there's your answer. sometimes those kinds of people just don't take advice and stuff well, she'll figure it out eventually though.

here's a wild guess...

she is aware that she needs to budget, and when you bring it up (and you make it sound like you do it constantly), you probably produce the reverse effect. one of the things that has always bothered me most about my mother was that she had a way of telling me i needed to do things just as i was on my way to do them. sometimes i think she would do it deliberately, so later she could say, "if i hadn't told you to go do the dishes, you wouldn't have done them at all". though i was on my way to do the dishes every time, the fact that she would go out of her way to tell me to do dishes made me mad, and it made me want to do anything at all but not the dishes. because you see, i could see for myself the dishes needed to be done, and i was taking care of it. she cut in, and i felt diminished, almost humiliated... because she thought if she didn't tell me these things i couldn't figure them out for myself.

you make her defensive because you're always pointing out her problem, and in reaction to that, she doesn't actually budget, because that would be doing as she's told, as opposed to taking action (and initiative) when it is needed. she's a big girl and you are not her daddy. let her figure it out for herself and stay out of it.

Maybe she gets mad when you tell her because, like you said, She knows she needs to.

Sometimes reminding people of their problems (especially the ones they are aware of) makes things worse

well its abvious she dun like u to talk abt it cuz she belives its her own business not cuz u got nothing to do with it but its cuz she feels like ur treatin her like a kid or like she cant handle it by her own so let her try to deal with it just absorve and help when she asks for thats all and dun say i told u before!

She's intimidated by something she has no idea about.