My cats like
Crumpled Paper Balls (those cellophane window envelopes are best)
Paper Bags
Cardboard Box Forts
Newspaper (portable!) Tents
Strings from Sweatshirt hoods (preferably tied on a stick)
Scribble Scrabbles (Frozen concentratrate juice plastic things)
Eachother
ME
*always cut...
So much switching around in such a short time can really mess a kitten up. Soft stools are not so much to worry about at really loose diahrrea, it may be she is just adjusting to the change in diet.
I suggest you stick to the wellness, (which is grain free isn't it?) and gradually...