If the issues were wear and tear, your friend should not be charged. If they were caused by your friend (her guest ir invitee) and are damage, she can be charged. There is no percent. It is either damage or wear and tear.
Asbestos siding was used on houses for decades and remains on many houses. There is no issue just because there is asbestos siding. The issue arises when the siding is being disturbed, repaired, replaced or removed.
If she made improvements, that was her choice. Any improvements or alterations belong to the landlord upon move out. The tenant gets nothing for making them unless the landlord agreed to it, in writing, prior to the improvements being made.
Also, sometimes what a tenant considers an improvement becomes damage to a landlord once the tenant moves out. The landlord can restore the rental to pre-improvement condition andcharge the tenant.
The landlord has 30 days in which to send an accounting of the Security Deposit deductions. The tenant is responsible to give the landlord their forwarding address prior to moving out.
If the landlord fails to send the accounting, the tenant can sue for the full amount (and somwtimes double or triple the amount) in Small Claims court.
To get the security deposit returned, the tenant must give the landlord, or his/her agent, a forwarding address in writing at or before the time the tenant actually moves out. The landlord must then, within thirty (30) days from the date the tenant moves out, 1) return the security deposit or 2) send the tenant a list of damages the tenant caused in the apartment, the cost of the repairs, plus any extra money left over from the security deposit. If the landlord does not return the security deposit or does not provide the written list of damages within thirty (30) days, the tenant can sue the landlord for double the security deposit by going to a District Justice's office and filing a complaint against the landlord.