Frustrated big sister

Danni • Mother to an Angel 💔
Okay so this isn't my relationship, but I need advice on how to help my sister. She has a new-ish relationship and her bf forced her to agree to get a dog with him. Mind you she didn't like dogs and she let him know that from the beginning. She hates animals so she wouldn't get one which seems responsible on her behalf. It's a puppy and the people he get it from said she was potty trained she isn't and it's driving her crazy. She has to range care of a dog she doesn't want and isn't hers. It goes in their apt all day and refuses to go outside when she takes it. It goes immediately in the house as soon as she gets back in. He won't compromise with her on anything. He wants her to get a job and stay at home to look after it. He wants it all but he doesn't want to take care of it. He works 8 to 9 hours a day and is "too tired" to take care of their responsibilities he brought into their home. He throws in your face all the time that it will be the same if they have a kid together. She's been taking care of kids since we were kids. How do I help? She called me in tears cause she doesn't know what to do it's tearing their relationship apart. The way it seems and it seems since they've had the dogs since Thanksgiving is that he is already picking it over their relationship. What do I do? What do I tell her? She's a very sensitive person and she doesn't really know how to stand up for herself. I just want to be able to be there for her and support her and her decision and help her out.