So about I week ago I invited a couple people to a party, including a couple mutuals friend of me and my Ex. A few days later she gets a text from one of said friends asking if she is coming to the party, she then texts me multiple times asking for an invite, I didn't want her to come (I'll tell you why in a second) but I didn't want her too feel offended so I gave her the excuse of "too many people are coming already". That night I told her friend some details about the party on a blog (dailybooth), which my ex then saw.

 She called me the following morning telling me how that wasn't a nice thing to do to her, she said I should of told her friend in private (even though me and my ex are not friends) and my reason for her not coming is crap. After a couple minutes of pestering I was fed up and I asked her if she wanted to know the real reason why I didn't want her to come, she ofcourse said yes and I told her it's because she can be slutty and high-maintenance, especially when she is drunk. I didn't want to tell her this in the first place because firstly, I didn't want to upset her and secondly, she will get very emotional about it, people will ask her whats wrong and I'll come across as a dick for having an opinion. 

So the day after that I went onto her tumblr expecting to find a post about that, and not to my surprise, she posted something along the lines of "Yay, I'm a slutty high-maintenance trap", which she obviously made so people will ask her why and then I'll come across as an arsehole in her story.  So I texted her asking her not to do things like that about me.

My question is was the way I handled it wrong?
Was I a dick to her or is she really just being well, high-maintenance? If so, how could I handle situations like this better?

nah..just keep not giving a ef would be my advice..who knows maybe to see a reaction from you is what she seeks

You should've told her in the first place that you didn't want her to come, that was the best course of action.
She asks "why?" you say "because i'm fed up with you" she asks "why?" you say your reasons.

And... what's the problem about coming across as an asshole? Your real friends know who you are, pepole who are closer to you than her know what you're worth, anyway, assholes finish first.

You're 15.

My advice is don't worry, by the time you're 20 you won't give a shit about your teenage years' shenanigans :P

I didn't tell her in the first place because I didn't want to upset her, she is actually a really nice girl, it's just mainly when she drinks she becomes very slutty.
I know but she just always plays the victim, and people then think I'm a dick until I explain to all of them, people I see almost every day in school -_-

Haha yeah I get that all the time, I don't really care too much, just wanted to double check if I did anything bad.

A little sexist but whatever, screw those slunts.

Sometimes you have to be an asshole to get your point across to some of these women.

I don't think I was an asshole to her, but I guess I might have to be if she comes up with any bullshit in the future.
Btw your sig always makes me chuckle xD

You handled it fine. I think it's time she grows up. She asked for the truth and you gave it.