Greetings,
Sounds as if Barney is not respecting Tilly's "dominant" position as the older dog. You should seriously think of stepping in and reinforcing that she is to be respected as the mature dog. This situation can easily deteriorate so that he could be biting/pushing her around at her in other areas of life. Especially when you are not around.
Support her position & clearly favor her over him. Either throw the ball & keep him on leash... or if he does follow commands off leash, tell him to "stop it" when he begins to harrass her. If he's pushing her around at other times & interfering... make him second again. Feed her first. Put him on a sit/stay by you until she is finished eating.
When you come home... pay attention to her first & if he interferes... eject him quietly & quickly, if you don't want to manage the sit/stay. If they're both allowed on the bed, he gets to stay on the floor for a while while you pay attention to her. Seriously, this can escalate & since she is older and not as strong, you have to enforce her position in the heirarchy.
Hope this helps as a start.
good luck,
toodles