I have just starting playing in a traditional Irish band (we’re a trio: fiddle, harp, and bodhran). I tend to play the harp more as an accompaniment instrument to the fiddle.
Even though I’m classically trained (voice), much of Irish traditional music is taught and indeed played without written music. This can be a bit daunting at first, but what I found is by knowing which mode/key the song sits in, you can do wonderful things with accompaniment simply by experimenting with chords (it tends to be a mix of I, IV, V, and vii, ii).
I’ve found that since I started playing in the band I’ve gotten better at this, and now when we’re doing a new tune, I just ask the fiddle player which key and I make up things as I go along, and it actually works!
Probably not the exact answer you were looking for, but if you have some time to work with your flute player, you might be able to come up with some wonderful arrangements on your own.