Crate regression, 6 month old

We adopted our new girl a few weeks ago and she's six months old. She was moved around quite a bit in her early life but she is so sweet and generally adaptable so far. We were told she was crate-trained but would cry a bit sometimes when first going in, then settle for the rest of the time. We found this to be true for the first weeks. We have her crate in the guest room and shut the door so our other dog, who can roam at night, wouldn't wake or distract her. The crate is not covered (we didn't have one) and we don't give any stuffed animals for safety reasons.

The first night we had her, I stayed in there until she fell asleep, giving a couple of treats and then leaving quietly when she was asleep. We followed the same process for the first week and let her cry a few minutes when she wasn't asleep yet when we left the room.

She has progressively gotten worse with it over the last week – she used to cry 5-10 minutes then it became 15-20. We're thinking it's because she's more attached to us and doesn't want to be separated now as time has gone on? I asked our dog trainer for some advice and she suggested trialing keeping the door open or putting a stuffed animal in there (her previous foster did say she liked that), so we gave her a stuffed toy at bedtime last night. She cried for over an hour with the toy in her mouth. I took her outside to pee and brought her back and she continued to absolutely howl and circle around the crate, in a way we'd never seen before.

We're thinking she was just not tired enough at bedtime (she slept on and off from like 7:30-10:30pm on the couch) and the toy may have riled her up for playtime instead of bedtime. Now we're afraid of rocking the boat and trying a crate cover or opening the door in case we have similar issues, but her crying periods getting longer instead of shorter over time made us want to try countermeasures.

She also goes in for a 3 hour midday crate nap where she usually cries a bit then as well. I'm dreading putting her in there today after how last night went but I know I need to try again and see if the issue persists.