How safte for a dental hygienist to put a cough drop in mouth while cleaning?

The official stance on this would be no, she should not have touched her own mouth and then touched yours, but the realistic answer is that you have not been contaminated with anything. I am sure that she did not get her gloved fingers all of the way into her mouth, she was probably cautious about placing the cough drop. Our hands touch worse things all day long and then we touch our own mouths. Think about the gas pump handle, any doorknob in your work place, think of how many people have entered their pin number on that pad before you.

You probably would have been exposed to more germs from her coughing than from her popping the cough drop, so you can rest easy.