Possibly food reactivity

Helloo! We have a lovely puppy (4months) for 2 months and a little. She's doing great so far but I'm concerned about possible food reactivity and how to handle it. I've noticed 2 things: 1. Sometimes when she's eating, I would call her name so she knows I'm coming and pick on her ears, tail, paws for seconds so she's desensitive of me touching her. As soon as I got close she got stressed or something and started swallowing her food really fast, so I stopped that. 2. When we're out on walks and eats something of the ground, I immediately try to get it out and that's where she becomes the devil, pulling away, turning her head around, getting on two feet and scratching me. I need to note that at home she doesn't act like that and when she picks a sock or something else, she lets me get it out easily. She also lets me lift her lips to check her teeth. So I need your advice on how to let her feel safer with me searching her mouth and how to handle this behaviour.