Hi there,
Not sure if I can help but would love to try! I am 38 with 7,5 and 3 year olds.
I see a connection between her being more apt to eat at the highchair if she can feed herself, and the fact that she's more apt to eat while you hold her: in her baby mind, it's less confrontational. When one sits across from another, whether in a job performance review or when being fed, it puts the feeder in the control position and the receiver on, well, the defensive. Maybe somehow, she senses that eating has become this "thing" and she's decided that she doesn't want to take part.
Having said that, I completely understand the feeling of wanting her to eat so that she can get all of the nourishment that she needs, and I can also see how you would feel some anxiety about wanting that to happen. You are only human. :) The thing that we all forget sometimes is that our children can pick up on that. As I'm sure you're learning, a huge part of motherhood is strategy and figuring out what motivates each child...which is a real challenge but it can also be super fun.
Ideas: at nine months, especially since she sounds really smart, she is SO ready and able to use a spoon and bowl herself. Babies R us sells those bowls with the suction cups on the bottom to eliminate the frisbee lunch scenario. Try to find one with the sectioned walls within the bowl to seperate the jarred foods from one another. Throw some chunks of baked apples in there, some oven roasted and skinless yam chunks, and some browned ground turkey! She will, most likely, chow!
One important thing to remember, which I actually read when I started this journey, is that we, as food providers, are only in control of two things when it comes to mealtime...#1 what we offer and #2 when we offer it. The eater needs to decide if and how much. I have found that the less "charged" mealtime is, and the less I try to "sell" it as this super great thing, the more and the healthier they eat. Just keep providing healthy choices, and leave it up to her. Soon, she will feel that she's this newly empowered, capable little person. I think that it will be a great experience for her...and a huge relief for you.
xoxo,
Fellow momma