Unless the computers are used by your family as well then she had no right to do that, you're 17. You may have had important documents on there.
And yeah, if you don't already, investing in a laptop would be a good idea. My mother has a family computer which I used to use but I've stopped using it to such an extent that I've deleted my account on it to free up Disk Space for my mother as I now have my own laptop, which I am using as we speak.