Kamen Rider has intermittent bouts of WiR syndrome going all the way back to Tackle's death (which I feel is a classic fridging). I don't think influence from American comics has anything to do with it.
I think in any action subgenre where creators feel they're writing to an overwhelmingly male audience, they're likely to decide that the death of a female character will have more impact than the death of a comparable male character. Men in most cultures seem comfortable with the idea that other men will die in battle, but a woman's violent death is likely to elicit more sympathy and perhaps a deeper sense of catharsis.
Modern Kamen Rider's courting of the housewife demographic has segmented the audience, such that writers need to presume an audience that may be as much as 50% female and probably older than the male audience that's tuning in. So if anything modern KR stuff is far less likely to fridge female characters, since the female segment of the audience tends to find such deaths upsetting.
So Modern KR is in this weird place where the stories largely stress the bonds of friendship and rivalry between male characters. Female characters largely fade into the background, assuming simple and largely unobjectionable parental, sibling, or spousal roles that the little boys in the audience can understand. Wakana's status as a female quasi-villain is a huge reversal of this tendency, so it's hard to guess where the writing is going to go with her based on Rider tropes.
Characters like Wakana are not unusual at all in comparable genres of anime and manga, though. Her archetype is not a gender specific one, either. In most anime or manga that have heroic undertones, any villain that evinces true sympathy or affection for the hero faction becomes very vulnerable. Said character tends to end up dying because s/he isn't willing to totally abandon the villain faction when s/he should.
If Wakana dies the way I think she will, then, it probably won't be just to make Philip mad. I would feel it's more comparable to the deaths of, say, Four Murasame in either version of Zeta Gundam, or the fate of Prince Heinel in Voltes V... or, hell, Kirihiko's death. These are all characters who are ultimately depicted as victims of circumstance, their inner nobility crushed by a monstrous and unfair society.
In this case, if Wakana dies, it would probably be to make a further statement about how absolutely horrible the Sonozakis and the Museum is. Kirihiko dies pretty much because he's not evil enough to be a true Sonozaki, he cannot completely disregard his ideas of right and wrong. Wakana is probably going to die because of her sister's total disregard for her well-being and her father's monstrous narcissism.
Of course, this is all speculation. As I've said before, I don't entirely put it past W's writers to cook up some way of plausibly saving Wakana. I'd still put that $5 on her not making it to the end of the show, though.
