Is someone able to help me understand my puppy’s behaviour, please 🙂

I have a 4 month old puppy (chi x jack russel) and I’m currently experiencing every puppy owner’s challenges during this age.

But there are a few behaviours I want to understand more so I can care for her in the way she needs.

1) She is usually behaved and calm when I’m not there. She doesn’t really bark and is okay being alone. She just goes to her crate and sleep! But when I’m there, she needs to be with me at all times. She’s very barky and bitey. Even if I’m just sitting on the table 5 feet away from her! She just wants me to be on the couch, which is beside her crate.

2) Today I found my cat’s old Christmas costume. When I put it on my dog, she suddenly behaved and just sat for a while compared to her usual barking and biting. I took it off to see if her behaviour has any difference between having it on and off. I put it back on and she calmed down again and started falling asleep while sitting up! Then eventually she just went into her crate and fell asleep, which is unusual. I usually have to close her crate for her to sleep. To make it even weirder, my cat just stared at her for the looongest time. Both my partner and I are confused and amused haha. Can some give some insight? I thought it might be comforting to her, as if she has a weighted blanket on. I never put a blanket on her because when she was 2 months old she would always resist/take it off when I put a blanket on.

Thanks guys!