some classes here start at 10weeks, but i chose a class that only allows them after 13 weeks (with a week for the vaccine to take hold) but held off going until she was 14/15 weeks just to be safe!
also remember, if your class is anything like the one i use, an all breed class, dont let them bully you into trainning methods you disagree with (like jerking by the collar and lead for a correction) while i see how that would get the attention of a rottie, it would hurt our kids! so harness her up, and don't let them tell you different unless you agree and feel it will be safe! and put something bright on your baby so the big clowns can see her- poppet got her tail stepped on her 1st week and wasn't amused bless her!!