Does it say anything on instructions of what to expect if cat licks it. On the one I use (broadline) it says" the cat may foam at mouth a little but should subside in short time. If it doesn't, seek vet advice".
Update! Willow spent the night in the garage and came in and ate!! She is acting like her normal self!! Mom says next year we are getting her the flea collar.
Flea collars don't work very well and some brands are downright dangerous to use. You can ask the vet for a different topical flea preventative product to use. Your vet would know which products are effective in your area.