Have you tried mixing some millet seeds and other foods together? Decrease the amount of millet seeds in the other foods over time. Hopefully she’ll get used to other foods and try them.
(With vegetables/fruits you can put some water on top and then put some millet on there)
I’m not sure it’ll work with your bird, but I think that’s how I got mine used to my food in the end.
(I’m also a fairly new budgie owner)
Let me know how it goes!