I think I had a hard time as a kid/teen with saying thanks and then sometime in my late teens/early 20s, after I wasn’t getting reminded all the time, it was like some switch was flipped.
I don't think she does it when she's selfish, she just never thinks about it. Part of her social anxiety, probably. I don't mind reminding her, but it does irritate me a bit even though I know it's probably not something she's able to help right now. Parenting is a minefield of emotions.
When someone asks if they can pet our dog, we always say it's up to her. Sure she cannot speak, but always has little body language and many times she's just not interested or looks uncomfortable or impatient to keep walking.
Even if somebody said I could pet their cat/dog, I would offer my hand for the animal to sniff first. If they don't like my scent, they probably won't like me petting them.
I was assuming that that was how the mom would react, since when I've done things like this as a kid my mom would burst out laughing, and when I've met other little cuties who did stuff like that their moms would laugh.