Here's an email from Barbara...
I was wondering if you ever heard or witnessed acts cat
like ours. I have been around cats my entire life, and have never came
close to meeting a cat quite like ours including feral cats. First when
she came into heat ( my mom lost her job and we had to wait for a low
coast clinic to have space ) she literately stalked me, hollowing at me
and "other" things. When I would leave the house she would calm down and
be fine, after we had her spayed she stopped that however she now
attacks strangers whom come to our door. Picture a cat attacking UPS
instead of a dog!!! If guests come into our home we have to lock her in
another room or she will bite, hiss and claw them. She is obsessed with
socks, she carries them in her mouth making mothering sound of cat with
kittens would. If we take them away and do not put them behind a closed
door she will go to great length to get to the sock. She is obsessed
with water including taking showers with us, she will sit in the tub or
sink meowing until we turn on a faucet to drink out of. Then the oddest
one is she gets obsessed with something she will not leave it alone no
matter how much you redirect her, you literately have to put her in
another room for a period of time before she unfixate on the object. She
runs up and bites my 4 year old sister for no reason besides she thinks
it's funny. If my mom is away from home for a night this cat will be up
all night into things, meowing and running crazy, if my mom is home she
sleeps thru the night. The scariest part is this cat isn't a year old
yet, and luckily she is a small framed athletic cat because if she was a
bigger build she would have already made a nasty wound.
Believe it or not I have indeed seen several cats like this. Fist of all, howling like she's demon-possessed is actually very normal when a cat is in heat. In fact, it's one of the key behavioral indicators that I look for since they don't drip blood like a dog would. The other behaviors are uncommon, but not unheard of.
One of the first things to realize is that animals think very differently than humans. For example, she's not attacking your sister because "she thinks it's funny." Animals don't have a sense of humor and don't mentally process behaviors in this way. She is doing these behaviors for many reasons, such as natural instinct, overstimulation, anxiety, and some sort of reward (such as a sense of having caught prey).
Cats are carnivores and predators so many of the behaviors we seen in them are related to hunting. Even the play of kittens is more along the lines of practicing for when they can hunt real prey. A cat can't anticipate the future like we can, so they don't know that they won't be in the wild bringing down mice and birds. Their instinct is to get ready in case that ever happens. Since kittens are learning and practicing for adulthood we often see them do it more frequently than adults. There are ways to redirect or discourage such behavior and your vet may be able to help in this area.
I will be honest in saying that some cats (and dogs) simply have a screw loose. Seriously! Psychotic behavior happens in all species, and I've known plenty of pets that have worsening aggression as they get older. These cases can be difficult to deal with as they require significant special attention by the owners and will need at least behavioral therapy if not actual medications. Hopefully your cat isn't one of these animals, because I've had to euthanize pets for severely aggressive behavior, especially when the attack unprovoked.
Don't ignore the behavior merely because she is small. Even a minor cat bite or scratch can become severely infected and size doesn't matter. I've received some pretty bad bites from small, young pets and those can be just as dangerous as from larger ones. If she isn't a year old yet she still has some growing to do and may cause more serious harm once she is older.
I would definitely recommend finding a vet who is skilled with behavioral issues and talk to them about what you can do to help with these problems.
