Crystal Gems are you friends or enemies? Touch stumps? You mean fingers?
Practically speaking, she's the size of a large city, with multiple rooms and corridors between them. But she's fitted with something called a Chameleon Circuit, which is supposed to allow her to blend in to whatever surrounding that she finds herself in.
I say 'supposed', because my TARDIS's Chameleon Circuit is on the fritz and she's stuck looking like a blue, Police Box from Britain.