
Well I would just stand there until they ahve finished and not allow the new one to pinch the girls fod until she has finished.
I feed five in the kichen and they all know which is their eating place and I won't allow them to investigate the others dishes.
When I ahve had a new pup or had a 9 month old back I didn have to keep watch that they didn't take liberties.
If your bitch doesn't finish her food in oen go give it do her at anpother meal time, a lot of dogs are fed two meals a day instead of one, and you could split his meals also.
Doesn't take long to stand over them while they eat.
As has been said your girl will soon realise that she must eat her food in a few minutes or go without until the next mealtime. You will soon find that it will be gone within a couple of minutes.