I really don't know how long they'd keep Umbridge in. The thing with the Dementors would definitely count, especially if she didn't get Fudge's approval first, and the lines-in-your-own-blood would count to...Attacking Hagrid, attacking Professor McGonagall--those definitely count. I'm not sure if her judgments under the Thicknesse regime would count because she was doing it according to the law at the time, but the locket and the eye were both stolen so that counts to. So, if we say 6 months each for the stolen properties, a year and a half each for attacking Hagrid and Professor McGonagall, I think between 5 and 10 years for cruel and unusual punishment, and between 5 and 10 years for siccing the dementors on Harry because a) innocent muggles might have been hurt, b) he was underage...does the Wizarding world have laws for the protections of minors? And anyway, he hadn't actually committed a crime. And c) it doesn't say whether she had the Minister's permission or not, so if she didn't, that would also count.
Aw, great, that looks so long now I read it. Oh well.
Bine: Molly's right (see below). Please read the rules. Since you're not yet sorted, take this as a warning.