The thing about a tambourine is that IT'S LOUD!! Far too loud in an acoustic session. Even in a miked concert, the tambourine is often handed to the 'non-musical' one. When in fact it takes some skill to play in time and play it non-intrusively.You did right to take the instrument away. Maybe there's another she can play in its place. The suggestion of the egg was good, although that sound tends to cut through as well.
I'm just waiting for someone to invent RUBBER-BACKED SPOONS. There is a lovely woman who comes to one of our sessions but insists on 'playing' spoons incessantly through the entire song and through all the songs. Oh - I forgot to mention that she pays out of time and the same rhythm, no matter what the song. No-one has told her to shut up only because she was married to a well known folkie who is now deceased.
C