Angurvddel
I am Large. I contain Multitudes
As for why Taylor specifically? There are reasons, though most are still currently spoilers. There's been fun speculation about it though, such as:
1)Khepri is also a sun god, associated with the rising sun and rejuvenation
2)Taylor made a pact of sorts with Ammy by giving her that friendship bracelet
3)Six degrees of separation. Taylor is (or will/would be) in a position to be socially linked to a lot of different people in a lot of different areas of the city. It makes her a nice hub to start with.
My guess is that Ammy is just a fantastic judge of character - which is much more in line with an actual Okami as opposed to Amaterasu. And frankly, aside from the Sun powers, Ammy's got way more in common with the 'wolf' mythology of Japan than Amaterasu-the-sun-goddess.
It fits extremely well actually, one of the things that Okami do is to guide people who are lost. That fits perfectly with her guiding Taylor back to camp in the first chapter. And then Taylor decided they were friends. And if you're going to fix the world and need a Miko, why wouldn't you pick your friend to do it?