Its like your Roxy is my Bella's twin!
I just got Bella spayed last Monday and she is also 4.5lbs and she had to have 3 canines removed.
I'm glad to hear you have the onesie...that was THE most important thing for Bella...and she also wore a cone at points. As far as eating, I left my Bella on her standard kibble and just added warm water to it in order to make it more appealing and so that it wouldn't irritate her gums. I did not feed her until 8pm the night of her surgery. And I only gave her 1/2 the amount that she usually has. My vet said the trick to avoiding a really upset stomach is to give her a very small amount of food...wait 20 minutes and se how she handles it. If she still appears to be hungry give her more otherwise just keep her hydrated. Bella actually went to the bathroom as usual, but my vet gave me the same information that Ellie May posted. And she was completely back to herself in two days. The vet even suggested that I take her off her meds because she healed so quickly.
Hope this helps!
And I know that your little Roxy will be just fine!