MaryJane, how about if you just tell her trust has to be earnt? And if maybe she can provide some structured exercises in class (if you're comfortable with those). Some of us can be more comfortable talking in class when it's required than in breaks or such when you are 'on your own'.. Only do this if you're really more comfortable with it.
Otherwise, how about if you say 'my Daddy was a loner too'? or such? (If he was-?)
My Mum shushed our sports teacher by saying she was bad at sports too
hmm..?
Or you might find a good article or book and give it to her?
It may be the people/teachers want to do good but don't know how to go about it. Sometimes teachers can overstep boundaries too, a girl told me her teacher wanted her to go meet her real dad and it was trouble for all involved, the dad didn't want to have much to do with her etc. Sometimes teachers just don't know better. Can your parents talk to her if she's making you feel uncomfortable?
I think some people are just naturally shy and forcing someone to not be isn't helpful. It's better to structure class so that kids can get to know each other, for example in languages or such, this is possible. It depends hugely on the teacher and her personality too..