You are lucky to have found the fructose problem early.
I have had IBS but not seriously since I was about your age. It got serious about 20 years later. I didn't find out about fructose until 45 years later. Looking back I can see how fruits, sweets and syrups have affected me. I have a suspicion that if I had reduce my fructose consumption at a younger age my IBS would be more controllable now.
The mystery is why recently diagnosed IBSers are not advised to remove excess fructose foods from their diet for a month or so. The effect of the change is rather quick. If there is an effect the diet can be modified accordingly. If there isn't an effect then continue to enjoy these foods! I sure wish I could. I still image the sweet taste of fructose especially when I am baking
Say - you might drop a short note or email to the dietitian with a copy or link to some good information on agave. I suspect she might be grateful for the knowledge.
-------------------- STABLE: ♂, IBS-D 50+ years - Science of IBS