I'm another who quit classical violin aged 16 because I was bored with it, picked up folk fiddle aged 26, and was shocked to find how much fun it was. Frankly I was also disappointed in my parents (who were folkies of the campfire-song variety) not having told me that folk fiddle even existed when I was a kid, because if they had then I might not have quit the instrument. In between I learnt to play guitar, which gave me a solid basis for improvisation and playing by ear.

Whichever way you go, initially you need to learn how to play notes to pitch, with correct bowing technique (ie. wrist action), with co-ordination between hands, and at suitable speed. Those are essential for both styles.

After that, a classical player needs to be able to translate from page to fingers with a minimum of thought required. That's a separate skill. Or a folk fiddler needs to be able to translate from known tune to ornamented tune with "lift" as appropriate. That's a separate skill. Folk fiddle also uses slides which are almost never seen in classical music, and may allow for spontaneous harmonisation with the main melody which is totally verboten in classical - separate skills again.

As separate skills, there's no reason you can't learn both paths. As Meg says, it's harder to learn when you're past 20, but that's just the nature of learning. They're separate though, and knowing one will not help you with the other.

For getting the basic techniques right, I'd highly recommend a classical teacher or a folk teacher who has trained classical-wise. Classical schools have spent 400 years working out how to play the violin/fiddle with maximum speed, dexterity, efficiency and tone, so there really is no substitute. I have a friend who's been learning with a folk teacher, and whilst the "feel" in his playing has improved, his bowing action remains appalling and the resulting tone is dreadful - having seen his teacher's technique, I then realised why. This is only technique though - what you do with that technique is down to the individual musician.

To be honest, most of fiddle playing comes down to imitation. You hear how someone else does it and think "that sounds good". Then when you find a similar bit in something you play, you can use the same ornamentation - if it works then great, if not then you don't do it next time round. If you're around Irish players and you're playing yourself, you pick it up. So I'd recommend giving her classical lessons and then drag her round the Irish sessions for fiddle playing, and she'll get the best of both worlds.

And shoot the piano teacher. Or force the piano teacher to teach her honky-tonk piano, blues and jazz, and improvising around a chord progression. If the piano teacher can't (or won't) teach that, find one who can.

Graham.