Well god DAYUM.
I'm convinced: whatever she says she is, Sylphy definitely classifies as a lower-case-g-goddess in my books. (Upper-case-G being the ones with true omnipotent and omnipresent power and knowledge - the kind that can unexist you with just a thought.)
It makes me wonder what happened that she is part of this system where she can become beholden to a mortal like this.
Also, I love her design in all three forms we've seen so far.
Addendum: I can certainly see why these summon cards are practically priceless. It isn't just the fact that you have such a powerful servant at your beck and call. It's also the fact that you can visit this fantasy worlds they live in, and stay there for practically however long you wish to, while only a few instants pass in your world.
Further musing: Now that we know about that wild time differential between their worlds, this means that the bath that Sylphy had been taking must have been at least weeks long. That canned fish stuff must have been some absurdly potent shit for Sylphy to have been taking a bath for that long to get rid of the smell.