It certainly wouldn't hurt to talk to the director, but maybe after auditions... sometimes they forget that shy children can be excellent on stage, so long as it is worded carefully like you are not begging for a role in the future... or better yet, encourage her to talk to the director and ask for any advice that can help. I was in theater for many years, and it's true, the outgoing ones and the ones who are favorites or even teacher's kids typically get the parts. But don't let that stop her. She's in middle school, and often by high school the group of kids that try out become smaller and more talented. Also, theater branches out, there is the techs, lighting, stage design, make-up and costume department, and as far as acting goes, they will experiment with musicals, stage combat, improv, dance... so encourage her to stick with it because those things are really fun too... and great for the shy kids who may not always end up with a part, but can learn other things that can be crucial for a role.
One thing we were told, was about a guy who was desperate for this specific part. He tried out and didn't get anything. Well, he showed up for rehearsal still every day and eventually an actor had to quit the play, so this guy knew the lines and act and was invited to be the lead, due to his perseverance.
Also, let her get involved in community theater! It may help her to open up and act around people that she isn't in class with.