Just say no, no, no.
Spend time today documenting who said what & when so far, & update every day with your notes cc any emails home.
You are being pressured into breaking the law.
Report to HR director, first verbally in a meeting (record this on yr smartphone/discreet device as a record to inform your written notes) & then follow through with an email detailing to meeting attendees what was discussed & any actions agreed, cc to yr home email. In a union ?, take yr rep in with you & cc them in on everything. Not in a union, take a friend into mtg with you.
I strongly suggest you contact ACAS helpline for advice about this before you approach HR bods, so that you can frame yr approach in such a way to get the response you require. As a ‘whistleblower’, you need to do this by the book to ensure your employment rights.
Foremost, you must protect yourself by using procedures in place, building an audit trail to show that you have acted reasonably & proportionally.
If you prefer a more direct method, then contact HRMC helpline to report her, but be prepared for some flak in your workplace as the disclosure trail will likely lead back to you.