[Well she's saying she does so that's good enough, right? Though her speech is kind of awkward and Rob's not sure what to make of it, but he's not going to be rude and comment about it.]

More generally, the ingredients you use have to share a magical effect. In this case, blue mountain flower and wheat both share the effect "Restore Health", which means they'll make a healing potion. They also happen to share the effect "Fortify Health", which means that these healing potions will also allow the drinker to survive more damage for a short time after they drink it, which could be a nice bonus in an emergency. They each also have two other effects, but since none of those match the potion won't have those effects. Those other effects aren't very useful here anyways so it's not a big loss.