Hello Shiva: Radiosurgery can be done as long as the tumor doesn't get much larger - the 22mm part of it is getting there + you need to have the radiosurgeon look at her MRI re: the position of the tumor in the brain. The only problem with 'watch & wait' is if the tumor grows to approximately 3.0cm, they would not be able to do radiosurgery because after the treatment the tumor 1st swells, then begins to die. So if you wait too long, then surgery will at some point be your only option. Now, the guessing game is that some tumors grow so slowly it may never cause a problem, some may stop growing altogether, some may grow more quickly - there is a 'gamble' factor involved with 'watch & wait'.
Some people have very few symptoms until it is quite large, whereas others have balance problems, facial problems, vision, etc. Everyone is different.
I hope this helps, Nancy