Ok, first things first if you want some advice theres some questions you need to answer so we have a fuller picture. I’ve seen this happen to foreigners in Asia before and in just cases it was resolved with a financial settlement. In this case, if you have the liberty please answer the following questions. For the record, I also highly advise the first thing your friend does is get a lawyer. Straight away.
1: Has the woman in question submitted a formal request to the police to proceed with pressing charges. If not then you will want to nip this in the bud asap. If you have a lawyer have him or here reach out to the afflicted party as a mediator. This is far preferable to the other option: a visit by the police.
2: Whether you have or have not done anything wrong there is no such thing as a good encounter with the police. If they have record of an arrest or an investigation it will make renewing your ARC/Visa extremely difficult even if you have done nothing wrong. Whilst they might not outright cancel your VISA they can simply choose not to renew it or issue you a new one at their own discretion if they decide they want to get you out the country in a passive way.
3: Evidence is everything in these kind of cases. Did she get a physical examination after the alleged assault ? If she did not it will be her word against yours. These kind of cases will examine the tiniest detail. From hair to skin, to abrasions to semen, bodily fluids, signs of forced entry etc… an examination can reveal a lot. If as you claim the boyfriend is pressuring her into making a false claim then this will be revealed in time.
As for counter suing her this will be nigh on impossible. Why? Just as the burden of proof falls on her shoulders to prove that you did commit the assault the burden of proof will fall on yours to categorically prove 100% that she lied. If the former cannot prove the latter than how can you prove she is lying. Often these counter claims would never make it to court as it’s a simple case of he said she said.
5: If she is Taiwanese she can do a lot of damage. She can spread rumours on social media, contact your workplace and tarnish your name. Check that you have an embassy here in Taiwam as they will be your lifeline if you are arrested.
6: If a settlement out of court cannot be reached you must ask yourself how far will you be willing to go to defend yourself. If you are arrested can you handle that? Then if you are indicted and sent to court could you financially handle that and possibly bail? Lastly, even if it is a 1% chance you must consider could you handle spending time in jail in Taiwan ?
7: In these situations even if we imagine the worst case scenario of being arrested, indicted and found guilty often these cases are a year or less of hard time. Especially important to consider also is that if you have a clean criminal record for first timers will usually be given a suspended sentence. So no jail time.
8: If you work in a school even a rumour will be terrible for you because the school will drop you, fair or not, as they cannot be associated with such things. It is the way unfortunately in many Asian countries that the assumption is of guilty until proven innocent rather than vice versa in the West.
9: Do not text her, call her at all. Why? Because you don’t want a harassment claim against you along with everything else. Get a lawyer and let him do his thing.