Women (and I speak as one) do this sort of social multitasking with each other constantly. Some are worse than others, but I think we're sorta hardwired to do it as a gender, and technology only makes it easier. So while I agree with you that she was being totally rude, keep in mind that she may not have intended it that way and might be really surprised by your reaction.
Uh, no (and I speak as a woman, too). This is not “social multitasking.” This is rudeness, procrastination, denial, and assholiness. He’s already told her that he didn’t like her going off when she had asked for his help. So she knew he didn’t like it but did it anyway. And then she’ll blame him? He’s lucky she’s just his GF. Drop her now.
I'm a woman, too, and I have NEVER done that. I think it's just plain rude, and very immature. If I ask someone to help me with something, I would never proceed to spend the whole time goofing off by texting and talking on the phone with someone else. It's childish and simply insulting to the other person. He's wasting his time to try to help her, and now she's mad at him because she squandered all of that time.
I have lots of female friends who have high pressure jobs---in that THEY are the only people who can solve the problem. One works for a cancer hospital, for instance and another is a social worker. Their jobs call them all the time. But, if in a social situation, they will just look at the phone, make sure it's not an emergency and then call the person back later. The behavior may, however, be a generational thing. All my of friend's kids feel they have to answer every bloody text and call they get. One can only hope they'll grow out of it.
And that's why she is now upset and was crying earlier, it's due tomorrow and I still have no inclination to help her with it. She's lost a whole letter grade on the test because of this and will not have her late assignments ready either. Ohhhhhhh..... well.......
Do NOT give in. Geez, can you imagine being married to this girl? Anytime she doesn’t like something she has to do, she’ll try to stick you with it and then blame you if it’s not to her liking. Again, drop her. Drop her like a rock.