First off, we have to deal with her delusion that she's always just one day way of being packed off to an assisted living facility after the longed-for nightmare of succumbing to rampaging senility becomes reality. Given that thirty year old Elly thought that she was an old, old lady far past her prime, it would have made sense to assume that she hates being reminded of how decrepit and fossilized she isn't even if we didn't have strip after strip of her wanting to let that sort of milestone pass by in silence.
Second, she cannot get it through her thick skull that her friends want to celebrate the happy occasion of her still being around, not hammer home the fact that she's oooooooooooold and ugly and has never done anything with her life. This irritating tendency isn't just because she's a morose twit who can't see the good in a situation or because she's a morose twit who is always astonished when others can. She's also a morose twit who can't wrap her head around the fact that celebrations are for other people. The same idiot who blasted Mira for daring to state that weddings are for the families of the bride and groom can't think along the lines of birthday parties being an occasion for friends to come together to celebrate something good: the fact that the poor dear who can't seem to find any satisfaction in a blessed life is still around and thus has a chance to finally clue in and see how great her existence is.