Probably the best thing would be a tremolo, but given all the different note lengths involved (and my amateur musicians who are not used to seeing tremolos at all) I would prefer to stay with the trill, if possible.
Should I flip the first tie? Move it up a bit so it sits above the trill note? Make it bow more upwards?
(Or, which of course would be the easiest: Am I missing a setting in Dorico to avoid it in the first place?)
I would personally arch it above to have it avoid the little note.
To make it less pronounced, you could move up the endpoints of both ties a bit (1/4 space, for example), and then increase the middle height of the first tie.
I would not flip it if I could choose.
A tremolo on the separate values, not tied, would perhaps be “better”, also because you are not technically playing a single long B. But you made it clear why this should be avoided.
