Lab r generally friendly dog, so she needs to find out why this pup is behaving aggressively. There may be some medical reason. But most probably its a behavioural problem. The particular problem that u have mentioned has developed becuase of reinforcement of negative behaviour. In simple language the pup has learnt that by bitting he can get treats!
She needs to restart the training sessions. First of all she must show to the pup that SHE IS THE BOSS, not the pup. Many blogs r there in dog training section about techniques to become alphs over ur pup. Do read them & tell her to follow the tips. He will start to listen to commands.
Then she needs to correct this bitting behaviour. First let him play for some time & be tired. Now she must stand right infront of the pup & command him to sit. If he does so then give him a treat. If he doesnt, she should walk away without any treat. If he tries to bite, she must very loudly & angrily say a NOOO & walk away ignoring him totally. She must put the treat back at this time. In the beginning he will behave aggressively, trying to bite. But she MUST NOT give anything to him, not even attention. Ignore him totally. If he still tries to bite give him banishment. She must find a place where she can put the pup for banishment. Banish him for till he calms down. Then let him out. Try again after couple of hours. This must go on till he learns that he can earn a trat only by obeying commands, not by bitting or nagging.
If he sees a biscuit in her hand & start bitting to get it, she must immediately say a no & eat the biscuit herself. He must learn that he gets to eat one when he behaves properly & when SHE wants to give one, not when he asks for one.
Hope this help. Do keep us updated.