I'm working on some writing on saints and surprisingly, I can't find anything online telling me what Zelie Martin is officially the patron saint of.

I've found 'unofficially, of the domestic church.' I thought I read long ago she's a patroness of lace-makers but I can't find that now. One page said she's a saint to pray to regarding breast cancer but I'm not clear whether she's officially a patron saint of breast cancer.

Saints don't automatically get a patronage when they're canonized. Mostly they arise out of popular devotion.

Thank you. I had actually asked elsewhere if it was 'official' or simply arose from enough people deciding it.

Sometimes there is an official proclamation, but not nearly always.