The only thing I can think of, since you physically can't shrink or grow your actress playing alice, is to shrink and grow what is around her. Since this takes place in a court room, one could somehow transition your courtroom scenery (lets call this scenery 1) to a 2nd  courtroom scene is all based on painted drops. (Say there is a Bench, a jury platform, the witness platform and three large windows that are all 3-D for scenery 1) When you replace this with scenery 2, make all of these things painted, and just "grow" the drops from the floor to the ceiling so as to make Alice appear as if she is shrinking. Make up enormus 3-D peices that can be pushed on from the wings, like the bottom of the legs of chairs, or characters feet that are surronding her. When this transition from scenery 1 to scenery 2 is done, you can continue the play with the voices of the characters as if they were coming from above Alice's head. She will have to be the facilitator here so make the audience beleive that she is listening and talking to the characters above her. There will have to be some willing suspension of disbeleif here on the audiences part as well, but the overall effect should be pretty good, it will look like a tiny girl in a HUUUGE room. In terms of her growing back to normal size, or even larger...can you do the same thing, but just screen the stage for a minute with smoke or some distraction to the audience and drop a HUGE pair of Alice's legs down with the hem of her dress visiable and her black shoes?

I would love to hear more.  I need all the ideas I can get!

The version of Alice that we did was a combination of Alice and Through the Looking glass.  Alice only grew and shrunk during her time in the hall.  My husband created a triptic flat that had doors of different sizes .  An crew member stood inside and turned the flat to show the different sized doors when the actor (who happened to be our daughter) walked from the table to the doors.  He also labored over a table which had legs that extended and shrunk ... this was no small task and is still a remembered headache.  When it worked it was wonderful and that was two out of three performances
here is the link to my drama blog with some pictures although unfortunately I have none of the shrinking expanding table or doors  :(

http://dramamamaforever.blogspot.com/

The old Eva Le Gallienne and Florida Friebus adaptation (available from Samuel French) is FILLED with incredible suggestions for the special effects in Alice in Wonderland.

Even if you're not using the same adaptation, it would be worth the minimal cost to buy a single copy of that script and peruse the special effects directions given at the end of the script.

It's pretty amazing - and, because it was performed decades ago, it's all do-able without a lot of 21st century equipment.