Should have done your due diligence before selling her the car. You didn't, that is all on you.
Now if she did not make payments that is another thing but the excuse of, "we did not do our job" sounds like a you problem.
Dealerships have been known to let you take the car and then call you back in order to renegotiate the deal over some bs.
Sounds like there wasn’t enough time for her to miss one payment.