Hi!
Welcome!
Congrats on your new addition. 3 1/2 months, they are so stinking cute at this age!! You don't need to give her anything else if you don't feel comfortable. I give Cheerios, apples, carrots besides a couple of different dog treats.
I try to not over do it, but DH doesn't seem to be on the same page when it comes to 'food' for the kids.
Just introduce things gradually to see if something might not agree with her tummy. There's a list posted somewhere on here with foods to stay away from. Grapes, onions, chocolate are three that come to mind.
The humping and growling to protect her greenie are dominance displays and of the 2 the growling is the one I'd address. If she wants to be boss over her toys that's ok, just be sure she never does it to a person. If she does she need to be stopped immediately. As for the growling, it shouldn't be allowed. She's telling you it's hers and you better stay away. The fact is she needs to know, Mommy giveth and Mommy can take it away. You should be able to take away any treat, toy or food at any time without her growling. It sounds like she sees herself as the boss right now. You may want to contact a behaviorist about how to over come this, because it could lead to biting. For myself, I've had dogs all my life, I'm not worried about getting a bite or two if I'm teaching submission. But I can understand were someone new to dogs might be. I'm sure you'll get a lot of good advice here, just use some common sense when apply that advice for your specific situation and you'll be just fine.