Ahh this reminds me of me ^_^
Several years ago, I had a favorite author, who now changed her penname and I lost contact with her.
She is with me, as you are with your supporter. I asked her to give me her opinion of my first fanfiction (the original is up at FF.net... it's kind of a horrible read... Nothing to Live For)
Well she was really really kind, but to me. No matter how you sugar coat something, the truth hurts. I still remember what she told me. She said my grammar needs a little help (as always and still do), I need to be less specific on certain things, and adding detail on where it counts. And, she said that my plot was going into two different directions. That it's breaking away from my original plan.
Which is all true. She said it nicely, but like I said... the truth hurts.
From a personal experience, I can safely say; Just tell her. My author made me a better writer by telling me her opinions. It's never too late to improve creative writing.
And you might wonder did I get angry with her? Yes, I did. I was selfish to think that my story could ever match up to hers, and when she told me... I was heartbroken. Which made me give up on fanfiction for a while, but hey I made a comeback.
Enough of my stupid story, the point is. If you really want to see your supporter improve her creative writing, tell her the truth does wonders.
You might get a bit of a bad response that might make you feel a little guilty on the inside. But tell her don't give up on writing, keep trying, find new ways of interpreting ideas.
I bet, she'll come back and thank you when comes to her senses.
Good Luck Lady Sianna!
For me, I never got the chance to thank my author for telling me the truth =( She's made me the author I am today, and I'm still trying to look for new ideas on interpreting details.