I noticed some of the same changes in my son when he discovered the world of on-line community. Rudeness and inappropriate language is standard issue, and his on-line communication style morphs to match whoever he is interacting with.
This is quite normal, I think. Kids want to fit in. They want to identify with their peers and be accepted by them, and, for better or worse, the way they usually do this it to imitate them.
I say that just to reassure you that your daughter isn't outside the norm, and that once her teenage years pass she'll hopefully mature into a person whose principles more closely align with the examples that the role models in her life have shown her.
That means you've got a tough road ahead of you. There will be a lot of teenage angst and I hate yous and rebellion and challenges and all the other things that young people do as they move through the inevitable and necessary process of separating from their parents and becoming independent.
The good news is that it sounds like you are taking the right steps. If being on the iPad causes your daughter to become rude and disobedient, there must be consequences. She has violated rules that she knew she ought to be following and you now know you can't trust her to do the right thing without oversight.
When our patience ran out with our son's attitude, we sat him down and told him that we noticed that when he spent a lot of time on the computer interacting with his friends, he became very sullen and rude. Therefore, we must assume that the computer time was causing his bad attitude and we needed to take it away. He assured us that we were wrong and that he could have a good attitude even while keeping his computer time. We gave him a chance to prove it. It took less than a day for him to blow it (no big surprise). We removed the computer from his room for a week.
After that, we told him that computer time was no longer a right, because he had abused that right, it was now a privilege that he had to earn. Every hour of computer time had to be earned by doing chores, or getting good grades.
I would recommend that you sit down and decide exactly what the rules are going to be, and what the consequences of breaking them will be. Present them to her with calmness and firmness. How you phrase it is going to be important. Don't talk about how you feel, or put the spotlight on your actions. You need to focus the conversion on her actions and attitude, not yours.
Don't tell her that you are sorry you have to take away her privileges, tell her you are sorry that her interactions with the iPad have caused her to behave in ways that are not acceptable. Tell her you are sorry that she isn't able to make good decisions, and that you have to find a way to help her make better ones. And then prepare to batten down your hatches to weather the storm of her disapproval. Don't make any decisions when you are angry, just stick to whatever you decided to do when your thoughts were unclouded by anger or hurt. I have found that strong emotions tend to prevent good judgment.
One last thing...it took a few months, but our son's attitude improved quite a bit. Now he knows to police himself because there are consequences waiting for him if he falls back into sullenness or disrespect with us. I don't spend a lot of time monitoring the way he communicates with his peers, a little bad language is kind of expected and I don't want to turn it into a big deal, but I will do "spot checks" and I expect that anything he says or does online is going to be available for me to read. If the language is bad, he loses the computer for a day. So he knows that every time he uses bad language he risks the consequences. It doesn't eliminate his bad language, but at least I hope it makes him think about it more. He protests that it's "private" but at his age (he's twelve) there is, IMO, no "right to privacy", especially after it has been demonstrated that he is abusing that privacy which he was previously allowed.
