Though rather rare, but some females have difficulty showing their true colors. So instead of showing vibrant colors, they mainly show "stress" lines - but they are not stressed.
Here are 2 examples:
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Though the first female shows her color, yet the stress line is almost always visible. The second female shows an extreme stress sign but isn't. BTW, both are flaring.... (sorry for the bad pictures)
I don't understand how a betta can "choose". I'd isolate them in a dark solitary for a few days and fed a lot. Then exercise her to other females or mirror if you don't have another female. Once she gets really aggressive, flare her to a flirting male. She should respond to him.
When bettas get intimidated, they often remember the color and would be afraid of such color. This might be the case with your female.... not sure.
And bettas from dark colored spawns would probably never see light colored bettas and vise versa. This is why some people believe that contrasting dark - light colors don't usually fight. But the fact is, they're not used to such colors thus don't consider it to be a threat..... most bettas would flare at any color..... anyway, they would be less responsive towards such colors.... this is why they're easier to breed if they're aggressive.
IMO she is probably a turquoise PK. They sometimes look more green and other times look blue-ish. She is a PK because her caudal is very short compared to her body. If she only has 2 rays, she is probably a traditional PK - or what people refer to as wild or fighter.
VT females often have rather oval caudals and are rather long - about 1/3 + of the body. They usually have the same amount of rays as the PK fighters.
I wouldn't advise mixing CT to anything - unless you have a definite goal. It would take many many generations to get them to breed true again.
If you want to cross tail types, cross PK, HM, VT. they are easier to fix and IMO are easier to rehome.
If you want colors of your female, it doesn't matter what tail type you breed her to. Form and color are two different gene pools(?). I'd suggest green, turquoise, metalic blue, royal blue, or any metallic.