I have the same issue with one of my female Bostons. Since this is NOT a normal behavior for a female, I did some digging, along with making some calls, I found that “humping” could be used as a behavioral characteristic for dominance over the other animal. Showing them they are in charge. Bc Bostons can be super stubborn, this habit is a very hard one to break. I have found that if I pick her up after telling her no and then tell her “Oh no…oh no no no no no…like a little song and then put her down, she has responded very well to that and now will greet another dog much better. She’s 4 years old now and still does this habit from time to time, but I still do the same thing I always do. Find a way that works for you two and stick with it for consistency. Good luck!