Help - Major personality change

My youngest calico, Sissy, age 10 mo. has suddenly gotten agressive with the other cats and with me. I have had Sissy since she was just a few hours old and completely bottle fed her. Up until about a week ago she was very friendly and loving and got along well with my older calicos. Sissy has not been spayed yet. I think that she is in heat or is pregnant. I was cat sitting my granddaughters male cat that I thought was neutered but he isnt. Last night she just went wild. Hissing and scratching anything in site. I put her in a large crate with her own food and litter box and this morning she let me pet her head but screamed at me if I tried to touch her anywhere else.
Could this behavior be because of her age and having an un-neutered male around? Or from her being pregnant.
If she is still the same tommorrow I will be trying to get her into the vet.
Any info would be appreciated.

This is an article on Cat Aggression towards People. It may give you some tips. I'm not sure about the pregnancy aspect of it, but you really should get her spayed as it will eliminate a lot of problems for her.

If she's not spayed, you've been living on borrowed time... and it sounds like time has run out! Please make a spay appointment right away!

Originally Posted by trinettec

I put her in a large crate with her own food and litter box and this morning she let me pet her head but screamed at me if I tried to touch her anywhere else.

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Did she eat and go to the toilet? She may have other health issues besides not being spayed.