Post Spay (went well!)

Zissou was spayed yesterday and they called last night and said it went well. We picked her up this morning. She has the dissolvy stitches and only a teeny little scar that looks just fine! Yay!!
However, she has had diarrhea today. She made it to the litter box both times, so its not too terrible. The vet said its okay so long as it resolves by tommorrow and she keeps making it to the litterbox and its not bloody or mucusy or anything, which it isn't. What is causing it though? Is this common? She seems fine, is drinking, eating, etc. I put a little water in an old cleaned syringe and dropped it into her mouth sideways just because I am scared, but she seems okay aside from being scared.
She isn't licking herself to much. However, the vet's instructions say if she does too much you can buy or make an e-collar. How would I go about making one, if anyone knows? She has a regular nylon breakaway collar on, if that matters.

Thanks!

I had to collar my cat for a couple of days, which went over real big! I bought one of those thick paper plates, and cut a large enough hole to fit her head. Then i cut around the outside so it wasn't to large, just enough so so could'nt reach around to lick. Worked like a charm, and it was cheap.

If she isn't licking herself too much, I personally wouldn't bother with the e-collar. Our kitties never had one and they healed just fine.