Tara-
You have a two fold problem here. One the one hand you need to resolve the diarrhea, but on the other hand need to make sure the food she does well on is for large breed puppies. This is critical. Dealing with bone growth disorders on top of diarrhea is no fun.
Unfortunately, the first mistake you made was switching her food when you first got her. Although I agree that she should not have been feeding Beneful, it is always recommended to keep a new puppy on the same food the breeder uses for 3-4 weeks before slowly changing it. Puppies are usually stressed out from the transport to the new home and from being in a place they are not yet familiar with. Adding a dietary change on top of that will almost always stress the GI system more.
Also, correct me if I’m wrong, but it doesn’t sound like you switched her to each new food by mixing the old and new food for 7-10 days. Or at least you didn’t mention if you did. If you didn’t do a slow switch, that is also part of the problem.
You will likely need to put her back on Beneful for a few weeks, make sure you are not overfeeding, and see if there is improvement. If so then you can do a very very slow transition to a large breed safe puppy food of your choosing.
