Sudden personality change with female cat?

I was hospitalized for a week at a treatment center for depression and I left my mother in charge of my cat and her kitten, I just got discharged from the hospital and coming home I didn't find my cat anywhere I was heartbroken and started getting a little sad since I'm super close to her and I don't have a lot of friends neither since I'm homeschooled. She was pregnant when I first got her last time, the person that I bought her from never told me she was, I found out when I took her to the vets for an update on her shots. And by than they said she was too far long to do an abortion, so I let her have her kittens and found them new homes when they were weaned but I only kept one since it reminded me a lot of her mother. Anyways while I was hospitalized my mother let the adult cat slip out of the house "maybe" intentionally, and she's not spayed I was going to spay her when her kittens were weaned but than a lot has happened and I went to the hospital instead.. She's usually a very sweet affectionate kitty and always clingy towards me, when she slipped out she didn't come home for a week and by than I started losing hope in trying to find her thinking maybe she got ran over by a car or eaten by a coyote but I kept the side door open the whole time hoping she'd find her way home soon, she came home but with another cat, that looked way larger than her that came in the garage with her and when I opened the door she darted in and the other cat kept meowing outside the door until I went to the garage and shooed him away, ever since than she looked like she changed in her personality. She kept running around the house trying to jump the windows and find a way out again and also kept attacking her OWN kitten who is also a female, that she used to be very motherly towards. I had to keep them separated until my cat calms down, and when she would and I would bring down my kitten again she would end up stalking her, chasing her and attacking her. I don't want to have to give up one or the other... Is this some sort of territorial thing? But than again she didn't act like this until she slipped out.. Someone please give me a detailed description as to what's going on with my cat? Is this something that I should contact her vet about? I'm going to do that nonetheless I care about her a lot and it's heartbreaking seeing her from becoming a sweetest affectionate kitty to an aggressive cat that hisses and attacks you and her kitten... :(