In regards to the female Predators, their appearance has been... inconsistent but also very scant. To date, we've only seen three notable females. Big Mama, Sister Midnight, and Hashori. So in my mind... I chalked it up to different body types, with Hashori and Big Mama being females with a masculine and butch build. There are human females who do have this body type, so why not Predators too?
Now in the case of Big Mama and Hashori, they're more or less indistinguishable from the males.. until closely examined anyway but if too close, you're probably already gonna be dead shortly. But what if they're just... two examples of one body type?
As for Sister Midnight, okay, so she isn't canon but... still, she's just one example of a female Predator we've seen none the less.
Maybe I'm clutching at straws. I don't know.