She recently called to ask if she can get a dog, and I told her she needs to sign a pet addendum and pay a $25/month pet fee, and she was so happy that we would allow for it. 

Proposed pets (size/breeds)
4.)

If my offer is accepted we will do the rehab and market the house for rent starting at $750, no smoking, no pets( if renter insist on having a dog I will add $25 on top of base rent and a non-refundable pet deposit of $250)tenant pays all utilities and does yard maintenance.So, as of now I’m projected to net at $266.

Pet owners are not a protected class.

Folks are looking for pet friendly homes to rent!

My girlfriend and I use wondercide on our Pets and home.

I've seen many different forms of promotions to get a renter to sign early; gift cards, percentage off of rent, or something like a small deposit for a pet, etc. 

Did they have any pets?

Charge extra if you allow pets.  

Sure you can have a dog, here's the (reasonable) pet rent bill and a box of treats.