Bad tenant finally left. Deposit refund.

[Carol Hensal]

After several months of non-payment, and over $4,000 of lost rent payment, she's finally gone!  The unit is a mess and will need at least $1500 in repairs and clean up.  We still have $750 of her deposit that will be applied to the repairs.

Do I have to send her a letter of explanation about the non-refund of the deposit?   What if her whereabouts is unknown at this point?