Answer:
When Charlie became more intelligent in a rapid way, He was moving up the level of intelligence in a fast pace and this worried Miss Kinnian because she did not want a regression and also the fact that she may not be able to keep up with him since Charlie now functions at a much higher level than she is.
Step-by-step explanation:
In "Flowers for Algernon" by Daniel keyes, Miss Kinnian was Charlie's teacher at a school for those challenged mentally, she recommended Charlie who is challenged mentally to a team of scientist to undergo an experimental surgery to boost intelligence, she recommended him for the surgery because of Charlie's eagerness to learn.
After the surgery has been conducted, and with further help from Kinnian, he gradually improved on his grammar and spellings. He also started developing feelings for miss kinnian and was attracted to her. but because his intelligence was moving up rapidly, Kinnian did not want a reversal and also worried that she may not keep up with Charlie as his intelligence grows much higher than hers, This made her worry about the future of their relationship.