The humping is not always sexual ... she could think of you as a 'big chin' (which is about the highest compliment a chinchilla can give a human
) and she is trying to show she wants to be the boss {alpha chin} in that house. Humping between chinchillas, especially of the same sex, is often a way of showing dominance and deciding who is going to run things.
This is something you need to break her of doing. You have to show her you are the one in charge... you are the alpha chin ... every time it happens ... give a loud high-pitched "OUCH", followed by a stern "NO-NO" and put her back in her cage. Chinchillas are smart and they usually learn quickly.
As a rule, they don't miss what they have not had ... normally the breeding age for a female is 9 months to 18 months ... depending on the breeder, the size of the chinchilla, as well as, the weight and the color of the chinchilla. I do not put mine into breeding until they are a year old, weigh a minimum of 500 grams, and can pass the thumb test. With the ebony, violet and sapphire, I tend to wait until they are 18 months old, due to their size.
Jo Ann