Even if not, it probably won't be worth their time and money to try to enforce the contract.

Your "hold over penalty" of $50/day on Top of the rent(maybe not enforceable under Any circumstances)  does not apply, according to Your lease language.

The liens that would continue "clinging" to the property after purchasing at a Tax Deed Auction are government-related liens (i.e. code enforcement fines, etc.)  

Hopefully she either walks away or follows the occupancy rules but if not you need to enforce the rules.  

Being legal and enforceable are 2 different things in a court of law.Usually there is boiler plate language that says the broker/agent is not an expert relative to matters with ( and lists everything known to man usually).

And yes I've been a wimp when it comes to enforcing late fees.

Can a landlord enforce the 1st of the month without push back?

If you have financing on the property, the lender will [usually] see this as a simple asset protection move and not call the loan or enforce the due on sale clause.  

Usually there are a mess of senior liens (like city code enforcement, AR DF&A, and IRS) recorded at the court house that have to be delt with.

Then be prepared to hold up those boundaries or have a system in place for someone to help you enforce the boundaries.