I don't think it's that black and white considering the huge disparity in income between them.So Gabby has travelled to USA and is talking about getting Cam something nice for her birthday this month. You mean the flight wasn't the present? Cam is awful. Gabby isn't the best person all round but she does appear to be quite thoughtful (when she wants to be)
When a single selfie with a skin + me product pays for a year worth of flights while it's a considerable financial effort for the other partner, then I wouldn't shame them for not being able to buy presents on top of that. She could have obviously still done something special, even if it's just a nice meal or a day trip.