Though Grete still attends to him at this point, how is it suggested that she is becoming frustrated with the job of taking care of Gregor?

Grete can't get any help and doing everything herself begins to get to her. She goes into Gregor's room and quickly leaves, does her duty and gets out as quickly as possible. Grete tries to do everything she can to make Gregor more confortable, but she stops communicating..... she seems to think that he cannot eat normally, fit into his room normally, or even understand.