Convenience anxiety is a crap term. I get that it's annoying when it seems like someone shirks responsibilities and only does the fun stuff, but it's equally understandable why someone who is prone to anxiety would be able to push themselves to do something they consider fun and feel more apprehensive about the things they don't. I used to work with someone who would take 6 months off a year with mental health, but would spend the time having holidays and stuff while the rest of us covered for her. It was horrendous. But, when she got back to work, she was bleeping useless because she genuinely couldn't cope.
Don't get me wrong, it's irritating as hell when you also have anxiety and put up and shut up so to speak, but I don't think other people's anxiety is less valid, I just think they are less able to cope with it for whatever reason. Probably because they have never had a reason to, especially in Zoe's case, she's so loaded she could miss loads of commitments and not have any worries about the consequences. Most of us don't have that luxury.