Tenant not vacating

Hello Sir/Madam, We have a tenant (single lady with no kids or relatives) living at my parents house on a separate floor for the last 1.5 yrs or so. My Parents (who are in their 70s and 80s) thought they were doing a good deed by renting the floor to her since she was single and listening to her personal story, didn't consult me or my brother (who lives with them with his family). All good - since there are good people in the world and sometimes you go with your judgement. However, my parents made a mistake by not making her sign any contract/agreement with her or doing any background check. Just took her word since she felt harmless. Then about a year later, they had a lawyer prepare a rental agreement with standard terms like rent increase after every yr etc. and asked her to review and sign it. She refused to sign it since she didn't agree to certain terms like increase in rent etc. They then told her if she can't sign it then she should vacate the home and she agreed. Then after few days they had an argument related to some expenses, which bubbled up and she left threatening them of legal action for mental harassment. When my parents told me, I told them to calm down since she was leaving anyway. After couple of days she called cops (no FIR), they came and after hearing both sides, just asked both parties to resolve it peacefully. They asked my parents not to talk to her and asked her to vacate by following month (which was only couple of weeks away then). So now after 6 months, when she initially agreed to vacate it then refused later and now has been delaying it ever since by saying "I'll leave when she finds something else". She just pays the rent (same amount she was paying earlier) and electricity bill with direct deposit in my parent's account. We don't know what to do in this situation, my parents have been reminding her very politely every month since then, to vacate it ASAP so they can get the rooms fixed up and put it up for rent again. They had another argument with her few days ago over a minor thing where she threatened them again by saying she'll report them to police for harassment. Please advise what can be done in this situation legally, which is not too laborious on them. Thank you!