Ah, well maybe she was different.. I remember she forced loki ( i think it was him) back or something.. maybe thats when it was said that she was different.. I edited.. it was natsu who entered the spirit world.. not lucy.. :-/
Her magic to summon.. i cant really see it becoming much more than that.. Unless she has the powers to create spirits, keys, enter the spirit world, etc..
With what you said i sure could come up with some crazy .. guesses.. lol.. some are actually decent, too.. well, what you said and the layla disappearance thing..
Oh, has she even tried learning any other magic? I guess there was an omake where mira tried teaching natsu and lucy transformation magic.. cant remember how it worked, but i think natsu learned it, at least.. Just seems weird that her celestial magic would be so much more.. unless its like an upgraded celestial magic as i said before.. Although, creation magic wouldnt be too out of reach.. so just maybe.. lol
I dont want her magic to be something completely different with pretty much no connection to her magic now.. (in your guess, anyway.. so its hypothetical)