Security Deposit - withholding late fees

[Tami Lumpkins]

I (with two siblings) inherited some commercial property that was already leased out - in Texas.  The tenant is now moving out (end of lease).  There is a security deposit (that we did not actually receive - we did not get any cash as part of the inheritance).

Every month for the past year the tenant has been late paying rent.  The lease does allow a 5% late fee for rent more than 5 days late (and it was always at least 10 days late).  One of my partners was in charge of the finances, and never requested the late fee from the tenant.

She now wants to deduct the late fees from the security deposit.  The lease states the security deposit is for the repair of any damages to the property.

I do not believe we can legally (or ethically) deduct the late fees from the security deposit.  But my partner is insisting on doing it.

I just passed my real estate license exam, though have not signed with a broker yet.  I do not want to do anything jeopardize my license.

So, questions - Can we legally withhold the late fees?  And if my sister does it anyway, can I as a real estate agent get in trouble?

Thank you for any help you can provide!