Progressive – in NC – just added my girlfriend and will add her ‘learners permit’ daughter shortly

Just found out Progressive will be adding my girlfriend as a list driver only (GF is covered by Allstate) which increased my premium by a small amount. What worries me is her daughter is next – no telling how much that increase is going to be. She is 15 and has a learners permit (again, in NC). She just got her permit and it will be another six months or so before she gets her drivers license. Their Allstate agent confirms the daughter is fully covered under her mothers policy.

I sent Progressive the Allstate documentation for mother / daughter showing complete coverage via Allstate. But, Progressive is saying because we all live in the same household they'll both be added – thus an increase in my premium.

Is this standard procedure?

If either one was to drive one of my cars and have an accident they'd be covered by their insurance.

Why the increase to mine?

If it makes any difference I am 60 yo. No accidents. No tickets, etc.

And why hasn't Allstate increased my GFs premium since I live in her household? Does it not matter to Allstate?