Thank you for that additional information, that will be helpfull in allowing me to advise you today.
She can still make the compliant to police, although it is more difficult to prove, but they would still take it very serious and understand her reluctance to come forward.
As far as work is concerned. There are two options open to you. Both equally open to take.
The first option due to the very serious nature of the allegation, and as they work together would be to formally suspend the person concerned pending a full formal investigation. Take statements from the victim, the male concerned. It could be difficult approaching possible witnesses without leaving your company open to legal action by the male if it is unfounded. This why better for the police to do that.
The second option is very similar but without suspending the person.
Once you have completed your own investigate you can either dismiss the claim due to lack of evidence, or if there is proof, or the male admits , you would have to decide what to do. It is such a serious matter that really only instant dismissal would really be appropriate, anything less could ben seen and condoning what happened.