Mother-in-law Trouble

Don't know how to deal with my mil. She has consistently not respected things I've asked of her when keeping my son. For instance, while keeping him yesterday my husband asked for a picture of him and he was laying on his stomach. Something I've asked her repeatedly not to do, since he's still young and just turned 2 months old. When my husband said something about it her reasoning could be summed up as "I raised you, your brother, and sister like this all by myself. And he's at my house so this is how I'll be with him." I've been nice and tactful in person, have sent very respectful yet deliberate text messages explaining my concerns, and she has consistently brushed me off. I am a very harmonious person, and I have to be pushed to even raise my voice. I wanted to cuss this woman's soul out when I saw that picture yesterday. I'm at a breaking point and need some advice.