She snuck a cat in against our no pet policy, lied to us about it, caused significant damages, did not pay the last month rent, owed us $350 upon move out (above what her $700 security deposit covered) - sent us a check for this - then stopped payment on the check.

Did the previous landlord collect a security deposit, pet deposit, etc and pass those funds on to you?

I can't collect last month, I can't collect pet fees, I can't collect key fees, I can only collect 1 mo rent and 1 mo security. $2.00 - not happening

From what I have seen here on BP, I would say no pets, ever.

Other Income includes a service charge of 50/unit as well as pet fees and late fees for part of the units, but I'm really trying to get the Expenses down to a T.

FIX YOUR PETS!

. :) "Maximum Pre-payments While a tenant may have a pet, or some interest such as portrait painting, which may potentially harm the apartment, you are prohibited from the collecting as advance payments more than the first and last month’s rent, one month’s security deposit, and the cost of installing a new lock (M.G.L. c. 186 § 15B).

As for painting, improvements, pet ownership and the like, you have the same rights as any other homeowner.

There is a "No Pets" policy which my tenants are aware.

I did a rehab where the pet damage was so bad on the slab the concrete had crust in places.