He doesn't seem to care, and his calm, friendly demeanour has been quite a good influence on her when we are meeting new people. But over time, will living with a dog who IS fearful change that? How have you dealt with this in your own dogs?
So far it sounds like Bowser is not being affected but I would make sure to give him equal time out in public WITHOUT Juno, just so he can see things through his own eyes (so to speak). At least until he gets older and his temperament is 'set'.
That way his solid temperament can help Juno.