bitch in season

Question
7 month old bitch in first season keeps mounting my older bitch and she onjects. what should i do and how long will this phase last

Answer
This is a dominance behavior, not sexual.  Be very cautious of any possibility of developing aggression between these two or you may have an unsolvable problem.  Remove the puppy (7 month old) by distracting her; if this does not work, put a lightweight leash on her and use that to remove her, then ask for a trained behavior from her and reward that trained behavior.  GET HER SPAYED (ten weeks after her season is resolved).  This is not a bitch you want to breed and not a bitch you can allow to obtain any further dominance related behaviors toward your older bitch; if such a problem develops between the two, you will require expert intervention and possibly it may not be resolvable.