Lie. "Dog ran away, I'm so sorry" to her and "found a lost dog" to a no kill shelter as far away as possible or find someone who takes in animals, online. The subs dedicated to dogs would provide either someone willing or a resource that could care for a mistreated dog as you described. Your only other options would be to kick her out or wait out her transitional period. I transitioned for years, multiple times so my advice stays firmly with my first option because it's about the both of them. She cant knuckle down and fix her situation with a distraction like caring for an animal. Not a fan of dogs personally but there's no excuse for letting an animal created for human companionship suffer for a few hours of companionship a week. Life has all kinds of risks and I'd easily choose to lie in this situation. I guess its stealing too but taking proper precaution reduces the risk to negligible. Tl:DR lie. Lie to benefit the both of them.