is it her grandma from her dad's side? I'm sort of guessing that because the grandma keeps calling the mom "Dal Ja's mom," but she could just be crotchety

You should double-check this with vonnie_k, but actually that's kind of normal, for women to be called "[insert child's name here]'s mom." Or it was in my family; it was probably at least as polite, possibly even more so, than calling the woman by her name. So it isn't necessarily crotchety at all.

Do they call her wehalmeoni or chinhalmeoni? The former is grandmother on the mother's side, the latter on the father's side. (I had to google for the latter because, well, both my dad's mother and his stepmother died before he met my mom, so I never knew either of them.)