You’d have to prove that your neighbor was truly negligent for starting the fire.

If so, can I charge her the $75 for negligence? 

The deposit is for damage beyond expected wear and tear as well as any shortage of rent payment (if your lease is written properly).It does not cover carpets/floor wearing out, paint needed due to being occupied for an extended duration, any plumbing issues, not the result of negligence, such as slab leaks, cracked sewer lines, etc. 

The return on a 10 year hold time is going to make waiting a month or two negligible.

For the last decade it has been negligible in return which is why cap rates for instance have been at historic lows. 

Well, now they not only can't buy the car they want, they can't buy anything at all. again, anecdotal, but credit inquiries when being negligent and egregious do hurt purchasing power. all that said, to OP, no you shouldn't worry.

No security deposit shall be retained to cover ordinary wear and tear which occurred as a result of the use of the premises for the purposes for which the premises were intended, provided that there was no negligence, carelessness, accident, or abuse of the premises by the tenant or members of his household or their invitees or guests.

Things break in a home, and if it wasn't gross negligence (i.e. the water heater is 40 years old and falling apart), carelessness or some other act of purpose on the part of the landlord, the tenant is owed nothing in my opinion.

Did they do something unreasonable or negligent to cause the damage?

The cost of bigger panel if needed would be negligible.