It surely doesn’t sound like she feels unsafe at work if she is pursuing these types of conversation with you. If the allegations were unsubstantiated and you were deemed by HR to pose no safety risk, you were both probably counseled about non-retaliation. I would wonder about her motive for initiating these non-work-related conversations. Is it to potentially make amends or set you up for a retaliation complaint?
Technically, by saying you are trying to steer clear of her you ARE choosing to ignore her, but you shouldn’t have to engage in unwanted fluff conversations during break time with her or anyone else. You have a couple of choices. 1) Make a polite excuse, cut the conversation short, and leave the scene. You might even try a "kill her with kindness" approach. 2) Offer to buy her lunch and discuss the entire matter, being prepared to hear her out and reach a truce. Or involve HR in the discussion. Concentrate on moving forward amicably and professionally. Perhaps there are behaviors you both could change? You may be surprised about the results. You could end up being one another's biggest allies. I've seen it before. 3) Report her staff room conversations with you to HR in case she adds new allegations like retaliation to the prior complaint. Consider talking to your manager about the issue before taking action.