Need some help with new puppy

Hi everyone. Sorry this is long winded, but needing some help with my puppy. We rescued her a little over a week ago, and she is showing some serious rescourse guarding issues. She is the sweetest dog in the world, friendly with everyone and every dog she meets, so learning that she has this behavior is a little shocking. We noticed this behavior for the first time the second day we had her, over something she had found in the backyard. We tried to grab it out of her mouth as we didn’t want her to swallow it, and she snapped at us. It has only gotten worse from there, it now happens about once a day and it’s over anything. For example, yesterday she had her front feet up on the counter cause she smelled food, we are working on the “down” command, but she wasn’t listening so I tried to give her a gentle push off the counter and she growled and snapped. Another time she had found something in the house, we tried to “trade” like some people had recommended but she was completely ignoring us and ended up growling and snapping. And lastly today she had a lick mat that she flipped over and could not get flipped back, we tried to let her work it out but she could not get it flipped so my boyfriend tried to help her and she got extremely aggressive. Probably the worst we’ve seen. She is only 12 weeks old and it’s making me nervous that she’s already so aggressive. She shows no other behaviors like this, it’s like a completely different dog. We have been trying all the things we’ve seen online but it seems to only be getting worse. At this point wondering if it is fixable whether it’s with us or a trainer, since she is still young at this point or is it just managing it? Thank you all.