Learners make mistakes - it's what they do. Some go on to learn from them, and others don't.

The instructor maybe shouldn't have been giving the hand signals but, she may have had a shitty day or been sitting with the pupil from hell. That maybe doesn't excuse her behaviour, but it may help make it more understandable.

For me, there are bigger things to worry about on a daily basis than someone making rude gestures, driving badly, or even setting a bad example to younger/newer drivers, and I think you should forget about it.