I totally agree with Ruth0209. Don't make up some awkward excuse for not wanting to do it. Just say no. My response is usually a big smile and an apologetic but firm.... "No, I don't give out my secrets" and leave it at that. They always understand. If I know the person really well I say "Well, I could tell you, but then I'd have to kill you!" Always good for a laugh! (That must be a movie quote somewhere!!) You simply can't give out your secrets if you're trying to make money at it yourself.
what irks me is she doesn't wanna research about it. It just means she's not really serious about it,maybe just in it to earn a few bucks (easily, cause that's what she thinks it is... EASY!) I tell people I learned what I learned from the internet. And I'm still learning everyday, everytime i visit this site. It's a continuing process and if you do not have the passion for it, then you are not gonna succeed.
better yet, just tell her or anyone else, this "Baking cakes/cookies is my passion and passion, i'm afraid, is one of those things you just can't teach to someone else."
I did tell someone just about an hour ago that I don't have time now but if she is really interested in it I can give her a few web pages to check out. She looked at me and said, "I don't have time to look all that up and read it all, I just wanted you to show me!" I just stood there for a minute looking at her and then said, "It's really not that easy for me to JUST show you! Sorry, but I will not be able to do this."
Wow! I'd say she qualifies as clueless! Kudos to you for such a civil reply.
Good for you & I totally agree with Ruth0209. There is no reason to lie. This is not only your craft, but your business & people you interact with need to learn to respect that. And judging from that lady's response, right now they don't. And if you do ever decide to teach don't forget, $75 for beginners's lesson, $100 for intermediate, $150 for advance, 10 people minimum for class, & don't forget their supply list! 
Agree with Ruth ... why is it women always want to do the pansy-ass way out of things? 
We teach our kids to "Just Say No" yet our kids watch their mommy wring their hands, wimper and cry, and worry about hurting someone's FEEEEEEEEEELings. Stop sending conflicting messages to your children. Teach them to JUST SAY NO!
I also like KKristy's answer. Tell them you are HAPPY to teach them how to do it in the classes you are forming as a fundraiser for your son's trip. My teaching rate is $50/hour ... plan on at least 4 hours ... here's the supply list (and be sure to tell them to put Advil on that list for the aching back they'll have after bending over the counter for hours and hours to decorate these things).
I disagree that teaching them will cause you to lose customers. I've shared IN DETAIL with friends how to make cakes and cookies .... right down to the number of hours they will need to allocate for baking, for decorating ..... and they ALWAYS come back to me for future orders because they find out just how much work it really is.
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