Keep a log. Document each instance, especially verbal that doesn't create its own record. Write down the time, place, manner (verbal/text/email/etc), and what was said by whom, and note if there were any other witnesses present. Don't respond in kind. If possible, don't respond at all.
If it comes down to you vs. them, having a written record will carry more weight than your word alone. Filing a complaint is important to generate a paper trail, even if nothing is done about it immediately.
Keep in mind that if HR gets involved, their job is to protect the company's interests from employee issues. This might be helpful to you - if this person is also harassing other people, and you can demonstrate that, then she becomes a threat to the company's interests.
Stick to a simple, straightforward message: you are happy with your work and you want to continue working with your employer, but this other employee is interfering with your ability to get your work done and is causing you personal stress and inappropriately contacting you outside of work hours. Everything that you present should back up that message.
*Also, don't volunteer the log, don't mention that you're logging these events, don't bring it up. You don't have to hide it as if you're doing something secretive, just do your best to be nonchalant about it. It is merely an observational record, and it only matters if this issue turns into a fight. It is not a weapon, it is a shield.
If the moment comes when you're having a meeting about this with management and HR, and they're asking you to justify the complaint you filed, that is when the log becomes relevant.
The more things go in this direction, the more likely they are to join in. The biggest reason they're (at best) wishy-washy in this area is that they're trying to pull centrist votes.
If the apparent center shifts, they'll shift with it.