Talk to your parents, express your concerns. Especially as Ozzy is a young guy, what he learns now can stay with him forever. Give her an alternate "what to do if he jumps up," and explain that it would help you, as you are training him, and if she would do it, it would reinforce in the same way you are teaching him, and he'd learn faster. Perhaps your parents will back you on this, and have a word with her "this is our house, you must follow these rules when visiting."

Find some material on dog training, and give it to her for Christmas, for when she has her own dogs some day. Maybe she'll read it - put a bookmark in pertinent pages - and learn.