Lots of people make fools of themselves at company parties. Of course, this can't be an excuse.
Overall, what is considered normal depends on the company's and your location's culture. Where I live I have seen all kinds of inappropriate behaviour at such events and to some extent it is considered OK as long as the participating sides were all fine with it. I've seen people get so drunk they couldn't go home (I mean they didn't know where they lived) and had to be transported by somebody else. They weren't terminated but did inspire gossip and I wouldn't want to be in their shoes.
In your case, however, it seems you have done something that was not OK with your colleague, assuming she really got out because of you. But even if she didn't, hopefully you got the message - work parties are not like getting drunk out with friends nor are they like college parties.
At all company events, even when alcohol is provided/free, etc, you should absolutely not get drunk or do anything inappropriate. Many of your colleagues will be in the party to have civilized fun - they might have a drink or two but they won't be expecting things they ought to see at a college party. Also remember managers and HR representatives will be there and surely they will not be happy if they see you act unprofessionally.
Now, back to your case. There is a big chance your colleague does not want to remember about what happened last night. You can send an apology message (it can be an IM rather than an email) but don't insist so much that she talks to you about it. Language like "crossed the line" sounds too harsh, yet very vague to me. Rather, you can express your concern that you have acted inappropriately and apologize if you made her feel uncomfortable. Assure her it won't happen again.
If she says it's OK, don't dig in any deeper and leave it as it is. If it gets more serious - she raises it with HR, etc., be ready to own it up and promise them it won't happen again. It really depends on workplace and location culture how bad this is.
The most important consequence of this is that you shouldn't do it again. Remember that company parties are not like going out with friends to get drunk and hit on other people.