Need help with calming our 1 1/2 yr old cat down

We adopted a homeless kitten over a year ago and she keeps wanting to chase our other cat who is 13. I have tried everything, flower essences, feliway, and I now separate them as he doing this stresses out our other cat who is having medical issues. They are good at night and sleep on the bed the younger at the bottom and the older up at the top. They go on the patio together and sometimes are ok and sometimes the younger one jump on her back and bites her. She use to try to chase her whenever she jumped off the bed but has gotten better. They are separated during the day and are supervised the rest of the time. We are already getting a bunch of remedies for our older cats health problem and she has Trigeminal neuralgia which gets exacerbated with the other chasing her. We separate them most of the time and at night when we are home and the younger one is sleeping on the couch we let the old one wander around. I'm going to try nat mur 10 M and wondered if anyone had any other suggestions? We try to give both of them the same amount of love and cuddles but I have to try to calm the younger one down due to the health concerns of our older one...I think there might be a bit of jealously w the young one as she completes for attention.