mollymay, sorry I'm joining this late in the day, but your 1st couple of lines made ma smile. My ds called the world and his wife 'mama'. At 1st it was just me, then dh too, then grandparents, eventually a smiley stranger on the bus would be honoured with the title!
And just to reassure you, I looked after ds full time, and as we live a long way from family, he only sees them infrequently, so there was definitely no confusion, it was just his word. He also called loads of things 'ba' - book, his monkey, bath, food, I loose track, and I'm pretty sure he wasn't confused between a book and a stuffed monkey.
My mil obviously was delighted to be called 'mama', and I must admit to being niggled a bit, which is silly, because she was just getting pleasure from her only grandson. I'm so lucky in that all my in-laws are fantastic & very generous with time & pressies - maybe too much so with the latter! - otoh they don't see the boys very much.
It makes me feel so saddened to read stories like yours where a parent or in-law is so outrageously cruel/undermining & upsetting. Even if she does disapprove of you working outside the home, it's her job to be supportive of you & her son, but then that's clear to everyone. The situation sounds like it will resolve itself soon anyway, but I would definitely chew dh's ear about it & get him to have a word with 'mama' and put her straight on what's on & what's not.
all the best.