Older DD saw Philharmagic for the first time when she was 2.5. She loved the show back the and she loves it now. 3D graphics are awesome, sometimes you feel like you want to grab somthing from the screen. And your DD will feel the same too.
It's not scary at all! Yes, there are sometimes when kids might get startled by some effect, bug the show is great.
Last time DD 9mths saw the entire movie, and she even let me hold the 3D glasses in front of her face.
Two tips. Sometimes kids don't want to wear their glasses all the time, that's ok. Don't force her.
Also, I remember older DD getting startled by the bottle uncorking at the end of Be our Guest segment, where they puff air to your face with each flying cork. If you think that can scare her, make her look at you face at that moment so she's not facing the screen.
If it doesn't spoil the fun, there are videos in You Tube, so she'll have an idea on what to expect.
The show is great. Try not to miss it
Mx