Tenant asks for guaranteed for safety of their major appliances

[Jay Chen]

My tenant acquired a refurbished clothes washer in Jan. 2019. And it is broken now. She hired an appliance repairman not electrician to take a look and the repairmen said it's due to low voltage and damaged the washer.

So I hired an electrician to double check everything and the voltage and everything checked out very well.

Now the tenant in fear of replacing the new washer and it gets damaged again and now asks me to write her a guaranteed letter that the house electricity is perfect and won't harm her future washer. Or I will pay her the washer. Yes I require her to buy a brand new none refurbished unit.

Is this even right thing for me to do a guarantee letter? Any special clause or negotiation I need to do if I must?

Thank you!