astigmatisms are where the lens is shaped more like a football than a soccer ball - they can be very mild and have little to no impact. or they can be severe. they change the way the light enters the eye, so your DD may have had to move her eyes more to get everything (which she would do unconsciously) rather than keeping them still. the glasses will just correct the angle the light enters her eye and reduce the chances of eye fatigue caused by the astigmatisms. a very large number of people have astigmatisms and get by fine without treatment for it - they just may get tired eyes...

2 years is a long time between testing - most optometrists would suggest annual testing if there is anything mildly amiss - especially with glasses. vision can change, and glasses can end up being too weak or strong if not monitored.... i've had glasses since i was 13 months old, and had had annual testing since then. not once has my vision been the same from one year to the next. they are all mild changes, but enough that eye fatigue occurs if i don't get new lenses each year