Do you think it's papaya itself you don't like, or just the chicken/papaya combination?
Because if it's just that combination, if otherwise you'd like papaya, maybe you could find other papaya related foods to suggest she make. I wonder if there is such a thing as plain papaya soup? For example. This might distract her from the fact that you don't like what she cooked, and get her focused onto trying something else specific. I've never eaten papaya myself, and I don't know if it has to be prepared a certain way to help milk supply, but hopefully other PPs can suggest good ways to prepare it.
The other PPs have given you good suggestions also, of course. I might add to them that you could say that for some reason, the combination of the two flavors gives you heartburn. Or blame it on baby. Say that the milk disagrees with the baby when you consume the foods in combination.
And this would apply also if you specifically don't like papaya. You could say that papaya doesn't help after all, or that it does but causes you or baby to be ill, or whatever...and again, thank her for helping you try this and suggest something else for her to try.
She sounds like a really nice person who wants to help you, so I'm thinking that while she might be hurt about the overall situation, that she tried so hard to do this that didn't end up working, that it wouldn't be something she'd take personally and get mad at you about. Sometimes situations are annoying and that can't be avoided, but that doesn't mean that the annoyance is anyone's fault, and hopefully she's the kind of person who sees this. And to me, it sounds like she probably is.
In fact, I bet if you take the route of apologizing profusely for the fact that this isn't working out, like "I'm so very sorry, I know you worked really hard on this and I can't tell you how much I appriciate it, and it just kills me to say this, but [insert chosen reason why you won't drink it anymore]" I bet she would apologize right back, and eventually you'd end up laughing with each other about how weird and bizzare something as simple as food gets when you are pregnant or nursing.