Why does my 9 mth old **** zu do this hoppy thing with her back end against any legs, table legs etc.?

She is nine month old and she has started this kind of hopping thing with her back end. She does it against human legs or any hard surface. I have never seen this kind of thing before and have asked people who are in the know about dog behaviour. They can't tell me what is going on. Is it possible that she is coming into her heat cycle, although she has been doing it for a few months now.