Actually, I thought it was quite realistic and gave insight to both characters.
Grissom represents logic over emotion. He has said many times on the show variations on “listen to the evidence, not your emotions”. You could argue quite easily that Grissom really isn’t comfortable with his emotions; he’s certainly somewhat awkward in social situations and oftentimes doesn’t seem to understand his staff when they react emotionally. You see this a lot in the interaction between him and Sara but it has shown up when dealing with all of the characters at one time or another.
Lady Heather, on the other hand, is emotion over logic. Her business is built on helping people overcome “inhibitions” and “convention”. This could be thought of as helping them to listen to their emotions and feelings instead of their thoughts.
This explains somewhat of what is going on. Grissom is desperately keeping his hearing loss secret because he is afraid that he will no longer be able to function as a CSI if anyone finds out. He can only exist comfortably in that world of pure logic and science; he can’t deal with the world on any other level.
Thus, he desperately needs what Lady Heather is offering. She is trying (in her way) to bring him out of where he is and I think he realizes that. (Maybe not consciously, but at some level.)
Lady Heather is obviously quite good at understanding people; in her line of work she almost has to be. She sees what is inside of Grissom better than just about anyone, even the rest of his staff, and thinks it is worth bringing out. This is her attraction to him.
Now, in times of stress all of us retreat to our “comfort zone”. When Grissom hears about her being diabetic and using insulin, he immediately switches back to keeping the world at a distance and becomes the pure, logical CSI scientist. The evidence says that Lady Heather is a suspect so he immediately treats her as one.
Lady Heather, despite what she knows about Grissom, can’t understand this. She is the emotional/feeling one. She can’t understand how Grissom can know her and still suspect her. After all, if Grissom were listening to his feelings and emotions he would know she would not have killed anyone. She feels betrayed, as if he doesn’t trust her.
So, Grissom is reacting logically and Heather is reacting emotionally and neither can understand why the other doesn’t understand.
Just my thoughts.