Let her know asap what the new rent will be as this may prompt her to move in the fall instead of having him added.

Then once you collect the security deposit and lease from the buddy ... promptly return the security deposit to the tenant who left.That's what I would do.  

He did fight for a "prompt cure" meaning the back rent had to be paid in one year vs five.

I have no problem paying for mold inspection/remediation and commissioning this activity promptly.

Then we sent a final notice that we would be filing a claim in small claims court, attempting to garnish their wages, hiring a collection agency and doing everything we legally could to recover the money to pay for the damages, and they actually promptly paid the entire bill!

Nine times out of ten, your best and most effortless ROI on any SFR is going to come from minimal turnover and vacancies with a stable tenant who keeps the place reasonably clean and tells you promptly when stuff goes wrong, but doesn't demand immediate fixes. 

She had one issue with her apartment and we addressed it promptly.

If they delay moving out, and the unit is not available to rent to a new tenant, then they are also liable for the rent you lose because of the extra time required to clean and put the unit in rentable condition (assuming you do that work promptly).

My attorney was very prompt and he also replied me this morning that it doesn't make a difference if the tenant is section 8 or else, a 30 to notice is all I need. 

Please pay your rent promptly so you may continue to live in the unit that you now occupy.As per your rental agreement:-- Rent is due on the first (1st) day of the month.-- Rent is late on the second (2nd) day of the month.-- We allow a grace period through the fifth (5th) day of the month to pay your rent without incurring a late fee.-- On the sixth (6th) day of the month we charge a late fee of fifty dollars ($50.00).-- If we do not receive your rent in full in a timely manner, we will serve you with a 3-day legal notice, “Notice to Pay Rent or Quit”.