I am not a vet so don't know how you can tell there is movement in the gut but I have had a pig who was close to death, no appetite, had sunken eyes & had lost weight. I syringe fed him on the Sunday & got him to the vet Monday where he was given baytril incase there was any infection but he was also given metaclopramide to stimulate his gut with more of each dispensed to me to give him at home.
He would take between 30-50mls of syringe food per sitting & his poops were tiny like hamster poops. Once his appetite started to come back, he ate small amounts of veg & the difference could be seen in the size of his poops.
I find it hard to believe that SR food is totally absorbed & this is why there are no poops because i know of a pig who was totally syringe fed for months (on SR & CC) who produced poops.
I can't say i've heard my guinea pigs guts make noises except for when one had gas but like i say i'm no vet & can only give my own personal opinion.
I do hope your girl gets better.
I don't see why not as you know how much she is getting