I would not suggest Chef Mickey's for your mom. The cupcake is served during the regular napkin waving dance, and isn't especially for a birthday. I think that all of the buffets do this (at least Cape May does also do it like this)
Prime Time Cafe is campy and fun - but also individual. We had cousin Mikey and he was FANTASTIC. He talked to our kids, asked how old they were, etc. My son who was turning two during the trip answered "Two" to Mikey. We corrected our son and said that he'd be two tomorrow.
Mikey didn't care. He came out at dessert with a birthday cupcake and everyone in the section sang Happy Birthday to our son. DS loved the cupcake, but the individual attention was lost on a two year old. If your mom would like individual fun then I suggest them! (Food isn't my favorite, but the experience was great overall)