I use a CAF number to sign my daughter's federal tax returns on her behalf. Can I also use it to sign her state tax returns?

Depends if the state accepts the CAF number as an adeqaute power of attorney to sign the state tax return. A phone call to the state tax department should get you the correct answer.

I assume your daughter is an adult, correct? If she is a minor you don't need a CAF number at all.

Good catch, ebaines!