hot tub

Tenancy Types and Management

My tenant wishes to use my hot tub in the garden which was excluded in the terms of the tenancy.
She tells me that her insurance policy will cover it for damage - she has checked this. She is a responsible tenant with a 3 year old son.

My concerns are;
who pays if it breaks down
Whose responsible if an accident happens
How will I know whether she is maintaining it correctly, including chemical management and filter cleaning etc.
If chemicals are mis-managed dangerous bacteria could accumulate, or chlorine burns could result.
I feel that the risks would outweigh the benefits (to me), perhaps I should offer to sell it to her?
thanks for your views.regards Diane