Can you use her food for treats when training during the day?
When my pup was 8 weeks she wasn't acutally getting dinner in her bowl at all as I measured the whole days amount and just took handfulls of it throughout the day to do training, sometimes it was just rewarding her for lying calmly, but mostly it was for when she was following me, which they seem to do alot at that age and hey its a great way to teach heel!
peanut butter is supposed to be good but I wouldnt feed alot, though mine do get peanut butter and cream cheese (eww lol) in a kong if we go out they love it.