Wow so rude, What did you say?
In your shoes I would have been tempted to say "That feels really rude to purposely take the family photo when I was in the loo." If she apologised or whatever and if something similar happened again I would be tempted to say, exact wording ... "That feels really rude to purposely XYZ, a bit like when you took the family photo when I was in the loo at the last meal out."
If she did not apologise or accused me of being over sensitive I would just say "Oh well let me know when you go to the loo and I will get my camera out."
And agree with others, when she messages re presents, say 'I will pass it on to dh.'
I think people can only get away with this shit because they are allowed to.
I would almost be tempted to say loudly at the table (while grabbing the waiter) can we get another photo with all of us in as that MIL took the last one while I was in the loo!
And Maisy re 'couldn't find my phone at one point and she said to my son twice 'mummy needs someone to look after her',
I'd make a job - are you offering to look after me, how sweet!
and 'why don't you just give up your job'
"Well I earn as much as your son and the kids are both of ours so maybe he should give up his job!."
It just sounds like they are picking at you.
Maybe a more productive way to deal with it would be to speak to her woman to woman and say 'I feel undermined when you say ABC (examples of what has happened) and I know we can have a good relationship, you buy nice things for the kids and I help you out with good ideas, I organise family gatherings etc whatever... so wouldn't it be nice to be more civil and polite and friendly with each other,"
She will doubtless protest she is civil and polite and friendly so you can cite some examples, in your shoes I would end with .. would you feel good about being exuded from photos or having it implied to your kids that you needed looking after....."
Good luck.