Grete is shocked and in disbelief when she first discovers that Gregor had turned into a bug. She isn't exactly repulsed by him, just simply taken aback by his metamorphosis. She almost is in denial at first, and doesn't accept this to be true.
Grete starts to take on the responsibility of caring for Gregor, a responsibility that no one in the house really wanted to take on. She prepares him a bowl of milk and bread knowing that it's his favorite, and brings it to his room.
Grete peaks into his room only to find the bowl still full, assuming that he no longer enjoys milk now that he is a bug. She quickly realizes the fact that he now is a bug and slowly accepts him and his new form.
Grete happily gathers some leftovers and scraps and brings that to Gregor's room for him to eat instead. She assumes he'll eat this and enjoy it more since most bugs just eat scraps of leftover food. She wants to make sure that her brother doesn't starve and that he still gets fed.
After seeing that Gregor had finished eating, Grete comes into his room to clean everything up while he hides under the sofa.
Grete still checks up on Gregor and still takes care of him, however, she is gradually finding him more repulsive to even look as each day goes by. She is starting to view caring for him more as her duty rather than love. Every time she enters his room, he hides himself underneath a sheet.