YTA. This should never have been an issue.

I've been with my husband for 10 years and married for 5. There have been many family photos taken, and I'm included in the "appropriate" photos. And there are no photos of me in his grandma's house. She's a lovely person. She's kind and accepting and has never made me feel unwelcome. She'll pray for me when she hears I've got exams coming up. But I'm her grandson's wife, not her granddaughter. She's not looking for photos of me to hang up on the wall.

This isn't like an adopted kid, you're not just "not biological", you're not her granddaughter. She didn't help take care of you after your mom brought you home from the hospital, she wasn't there for your first birthday, she didn't watch you grow up.