DrWu

Sorry, I realize saying she has a B1 is imprecise. She has a valid B1/B2. 

Answered my own question... the answer being she may not need and interview...

I'm a USC. My Thai spouse has a valid B1/B2 in good standing but is due to expire in just over a year. Is there any advantage to applying for another one when her old visa is still valid? 

I'm a USC residing in Thailand and legally married (12 years) to a Thai national. My spouse has a valid B-1 used many times over the years (soon needing to be renewed). We are interested in bringing our granddaughter on a future visit. As a minor child (8 years old) I understand she'd need a passport and the usual for a B-1 application. My question lies in how strictly immigration interprets their own guidelines regarding "legal guardian and custodial parent". Does, for instance, a notorized letter of permission from her parents satisfy? I have low expectations but I'd kick myself forever if I didn't ask