Another way to put it into prospective - how much do we pay to take classes with Collette Peters, Bronwen Weber and so forth? I know I just spent a pretty penny to learn new gelatin techniques and carving procedures. I did not get them for free!
Either tell her you don't do classes or give away instructions, but if she really wants to learn recommend classes with the above mentioned people, Wilton and good online sources. Then thank her for her interest.
And yes, it is different from giving advice to a fellow cake person and a cake civilian. Cake people know it's a lot of work and at least, for the most part, have some sense of foundation. Cake civilians don't. For example, I'll tell my family members how to do some stuff sometimes, but it's lost on them. My brother once helped with his 18th birthday cake - SIMPLE piping. Yeah, at like two seconds he said - whoa, this is harder than I thought.