Thank you for that additional information, that will be helpfull in allowing me to advise you today.
There are several steps that you can take.
The first step is to issue your sister making these allegations and who is contacting your employers with a "cease and desist" letter. This letter demands that she stops immediately form harassing you and carrying out the actions that she has been doing. The letter would advice her that failure to do so will result in full legal action being taken against her, both civil and criminal and without further notice.
That letter can be sent from a solicitor so she can see you have taken legal advice on the subject, or you can send it yourself, if you do so send it recorded or registered post for proof of postage and receipt.
Once the letter has been served, if she ignores the letter, you can then report her actions to the police as harassment . The cease and desist letter will assist as evidence that she has been warned and ignored that warning.
You could also then on the civl side if thongs apply to the court for a non molestation order against your sister.
If the court granted this, it would place an injunction on her from doing what she does.
If she breaks the order, the police can arrest her as a brach of that civil order is a criminal offence.. For the first breach she is likely to be fined and subsequent breach could result in a prison sentence. If she follows the order she would not get into trouble so the onus would be fully on her to follow the order or else!