Stuck collar

Today I decided to try a Sentry calming collar on my cat Angel. She seems to be calmer and she uses the litterbox when she is in our room with the door closed and we have a plugin in there. With our open rooms and high ceilings I don't think we can afford enough plugins for the rest of the house to make a difference.

I've read about cats drooling or becoming lethargic with these collars so I had the whole family watching her so they could remove the collar if she reacted badly. She's never worn a collar but sat very nice when I put it on. Unfortunately I put it on too loose. She was doing great this morning so I left it on when I went to work since someone would be home in an hour and it was her sleeping time.

My son said she was hissing, then my daughter called because she was staring at her with her mouth open making weird noises and then she stopped moving. I had my son check on her and she gave him another open mouth hiss. I said that my husband needs to check her as soon as she gets home. He saw her walking around the basement and assumed she was fine, until about 2 hrs later when he texted me that Angel was just staring at him with her mouth open like she was going to hiss.

That's when it occurred to me that the collar was stuck in her mouth. She took off and he searched for her with soft food and catnip for almost an hour before he found her. As soon as he grabbed the collar it broke and he let her hide again. The collar was in her mouth for 3-4 hours.

She was shaking and he said she wasn't in good shape. He put soft food and water by her hiding spot so she could have time to calm down. She didn't come out until everyone was in bed. I come home late so I'm with her now.

She seems tired and a little nervous but ok if you move slowly. The thing I'm worried about is that she's avoiding opening her mouth very much. She doesn't react if I touch her mouth but she won't let me look. Should I be concerned about injury to her mouth? Or should I just give her time to relax and check when she's more trusting?

One corner of her mouth seem pink but she won't let me get a close look at it. She's still a little nervous.

Honestly, I'd take her to the vets. But I'm a relatively new cat owner, and freak easily.
Can you tell if the collar is the same size now as it was when you put it on her?
I'd be afraid she had ingested a piece of the collar, or (probably more likely), scratched the inside of her mouth with the clasp. If the later, her inside of her mouth is probably just irritated.
Is she eating? Good that you're trying the soft food, avoid dry food/treats, for now.

I know she did not eat any of the collar because I checked it over carefully and no pieces are missing.

She is being super lazy today. Maybe it is just her crashing from being so worked up. I think I will call though because I'm not sure how bad that powder on the collar is for her.

I didn't talk to Angel's vet until yesterday. I noticed her gums are black on both sides of her mouth. The vet did some research and had no concerns about the actual collar. She felt it was perfectly safe for cats.

As for the gums, she said injury should be swollen and purple/blue not black. The black could just be the coloring of her gums. I haven't looked at hers before but Peanut has black on his gums. Since she just had bloodwork done she said it's up to me if I'd like her seen. She has been sleepy since but today she got super playful.

For now we are checking her gums daily and trying to watch her eating. She eats soft food but I'm not sure if she's eating hard food or not. If I don't see her eat soon I'm bringing her in on Saturday.