Teal, mint, light colors, look good
I found for my dark bay (I asked this question right before you) that a nice pastel blue works. He looks very stunning
It depends on the shade of bay! I've seen some fiery red type bays that look really nice in black but the darker ones just get washed out. Icy colors, such as teal, mint, and turquoise, look very nice on most shades. Dark bays tend to look nice in red :) So you've got quite a few options depending on her exact shade!
I always have like putting bay horses in teal