[@shylarah]
Sounds about right
I'm lacking in sleep so my memory is a tad foggy

So cases like Feoras and possibly falk are rare since they were created singularly (I'm guessing in falks case) which is why the two are powerful. 
Though with Feoras a tad unstable at times.

[@Ojo chan 42]
I'm thinking per chance the girl was a kelpie and did not know it. That would make the child a full kelpie that simply grew up in the wrong world. Possibly a dying outcast kelpie took the baby there to be raised (kind of like a cuckoo bird) 
This is simply a thought in no way do you have to follow it

Edit: especially since that would change up your current character a bit

This is truly interesting to think about