First, the "I want that" is not, in my opinion, an order. I say things like that on posts all the time. But "I want" is not a "I am going to buy" or, even in CF land a "You must give me one." So on the "I want" post just reply - if you want to order one, you can do it via the website". If she asks in person, tell her you'll happily make and deliver one but you'll need full price.
For the ones she agreed to pay for but hasn't, even at discounted price, you need to send her a message saying, "Please can you send over the money for materials for the [pieces] I delivered last week." If she still doesn't, you'll need to be firmer, pointing out that you need the money as your business has costs.
This is actually a bug bear of mind. DH's job is one people often ask him to do as a favour for a friend or whatever. To be honest, he mostly doesn't mind and actually would find being offered money uncomfortable. But what never ceases to amaze me is how often at this sort of event people will make comments like, "[name] is so brilliant. I can't believe how good he is." (Really? Because you KNOW he does this for a living right so....?). Or they'll say things like, "if you ever need a favour, just let me know". I mean, how is that helpful? Are you going to do his tax for free now Mr accountant?
The last time he did this, I was completely GOBSMACKED to discover that at the bar DH was expected to pay for his own drinks. He provided a full on service for free and they couldn't even buy him a beer?!