Haha, you should try this technique of just starting a sentence and then finishing it no matter how many times you're interrupted. In your friend's situation she is doing it because she can't help it and probably doesn't realise half the time.

If you do it with a smile on your face, she will pick up on it and laugh with you, she will then stop and let you say your piece. It is much better to point out people's faults using humour :-)

Cg