My co-worker keeps sending me emails that are
unrelated to work. What can I do to get her to stop?

Your first recourse is to check if your company has an official email policy. Such a policy would likely include guidelines about sending emails that do not pertain to business matters. If so, communicate to your mail-happy cohort that you don't want to run afoul of company policy. Ask her then to stop sending you these missives so you can avoid any penalties. If they don't cease, talk with your manager or your human-resources department representative to see if one of them could help pull the plug on these unwanted communications.

If there isn't a policy in place, and if you don't have a human-resources department or a helpful manager, then you'll need to adopt a different strategy. The next time your co-worker sends you a message unrelated to work, email her back and, politely but directly, ask her to remove you from the mailing list. If you're fearful of offending her, and thereby causing friction in the office that might escalate and spark an ongoing problem, you could suggest that she send these messages to a personal email address. That way you can keep the peace without adding stress.