So good that your girl is with you now
Interesting to see how their relationship with the cat will evolve))
She also can not predict when she will want to go to the bathroom yet. She is so little and her bladder is tiny! They pee a lot at this age. Also she needs time to adjust to her new reality. Give her something tasty when you put her in the pen so she makes a positive association. Ignore the barking and praise when she stops for being quiet.
I'm sure there's no need for a diaper.. We trained our boy indoors, and had pee pads all over the area where he was allowed to walk + one in the pen where he slept at night. I wanted for him to see a pee pad in close proximity literally anytime he wanted to pee. After few weeks we started taking away one pee pad at a time and then moving the remaining one closer to his permanent toilet spot. I also praised him a lot for going on a pad.
He also still follows me to the bathroom every time but I taught him "stay", so he stops at the door and waits patiently now.
I hope your girl will adjust well and soon!