Susan, I have read through the only two walkthroughs that I could find, and I swear, neither of them makes any mention of lemons until the moment they tell you to cut one up! I assume that you've checked your inventory, to make sure that one didn't sneak in when you picked up something else?
I'll pass the word on to Tally Ho that you are having trouble--I'm sure he can tell you where to look.....
"Once you give up integrity, the rest is easy." Anonymous