Many thanks for your patience. The first thing you have to consider is her length of service. If she has been continuously employed at her place of work for less than 2 years then her employment rights will be somewhat limited. Most importantly, she will not be protected against unfair dismissal. This means that you can dismiss her or force her to leave for more or less any reason, and without following a fair procedure, as long as your decision is not based on discriminatory grounds (i.e. because of gender, race, religion, age, a disability, sexual orientation, etc.) or because she was trying to assert any of her statutory rights (e.g. requesting maternity leave, etc.).
In the circumstances it appears she walked pit rather than be sacked so it would be a constructive dismissal claim she would be looking at but again she needs 2 years service to be able to claim. Not sure why she is claiming sexual harassment but without any evidence it is unlikely that such a claim would succeed.
Also you have to think if she will actually go ahead with this. To make a claim and take it to a hearing costs £1200. Would she pay that much money when she clearly has no claim, or a very weak one? So the chances are that she may be just threatening you, without actually ever going to go as far as making a formal claim.
At this stage there not much you can do apart from wait to see where she takes this. She only has 3 months to make a claim so it is not going to be a long wait for you to find out if you are going to have to defend a claim. She will also have to go through ACAS first and conciliate with you before she can claim and I can discuss at this involves with you.
This is your basic legal position. I have more detailed advice for you in terms of the ACAS procedure and what you can expect, which I wish to discuss so please take a second to leave a positive rating for the service so far (by selecting 3, 4 or 5 stars) and I can continue with that and answer any further questions you may have. Don’t worry, there is no extra cost and leaving a rating will not close the question and we can continue this discussion. Thank you