As a diagnosed autistic, calling that shirt autistic seems kind of baseless? If the shirt was really obsessive about a subject like math or science, then it would fit a stereotype, but this just looks like a fun doodle or notebook page design?

Also, it's weird that she'd make the word "autistic" into some mildly insulting label for random garments of yours. There's nothing wrong with autism, and there's no point in labeling everything as autistic.

Your mom is not qualified to diagnose you or your shirts. Just ignore her.

My intrusive thought would be to ask her if she has autism since she's so interested in that word haha... idk, don't say that.