@Sep10trion If they can change it at all the "true form" literally becomes whatever they want. No point thinking about it. Shapeshifters might have original or base forms but lets be honest, you don't really need anything but what you need. If they are comfortable and happy in a form you like, they are just another girl or guy or attack helicopter.
Being attracted to females means that if a guy turns into a girl you will be able to date them. Its "effectively the same thing" in that as long as your specific interest isn't one of mental or soul or whatever compatibility the shape they currently have is all that matters. Thats why "straight" people can be into traps. What they need is all that matters and sometimes a vagina or lackthereof isn't a deal breaker.
Anyway as an Omnisexual it doesn't really matter to me so just enjoy what is without worrying about what isn't. If your just curious they seem to have been a female originally but you can't really trust someone who can change that AND is trying to smash. She's not exactly lawful good so who knows if she's the type to lie to get in your pants.