First if all here is a link to a summary page on guinea lynx with lots of case histories concerning the use of actigall for bladder stones. Some worked, wome didn;t....and right at the top you will see a warning that this is potentially hepatotoxic for hind gut fermenters such as rabbits and piggies. Nevertheless, there have been some notable successes.
http://www.guinealynx.info/records/viewtopic.php?t=93
I am intending to print out the page, plus follow the links to case histories and take it all to my vet for their comments.
Re the Xrays -Your vet shoud have checked there were no stones in the kidneys themselves. When Fleure had a urethral stone - the vet also made sure the Xray taken was positioned to include her kidneys and bladder. She had no bladder stones at all - but both kidneys contained several stones of differing sizes....the largest of which would not be able to pass down the ureter to the bladder and thence to the urethra. This is what governed her treatment as kidney stones are inoperable and just stay in te kidneys getting bigger if they are too big to be flushed through...hence why we tried to shrink them with destolit. We did test the composition of the urethral stone first to ensure it was calcium carbonate (which destolit has been successful with) and not calcium oxalate. (A US research project recently showed that the many piggie stones submitted for analysis were mainly calciumcarbonate...thus disputing the main test book reference (which despite being old is still used by many vets....my vet at the time included) that piggie stones are calcium oxalate.)
Cystease contains glucosamine - not potassium citrate - and is intended to help maintain the integrity of the bladder lining. This reduces discomfort, reduces the risk of infection and hopefuly therefore reduces the episodes of cystitis. Other things that help the bladder lining can be pearl barley gloop (boil up pearl barley until it is mushy, strain off and keep the sticky water/gloop and add cranberry juice).
Cranberry juice is thought to contain molecules that prevent bacteria from sticking to the bladder lining and thus is of more use in urinary tract infections...although it does cause a small short-term rise in urine acidity which also discourages bacterial growth.
Potassium citrate is used to acidify the urine in an attempt to help dissolve the stone and prevent futher stone formation
Uriflow also claims it can break up stones
And as I said above destolit/actigall/ursodiol has also been used to dissolve piggy bladder stones.
As to prevention of more stones forming - following a low calcium diet, use of filtered water as mentioned.
Some people use the chinese herb Shi Lin Tong
Again guinea lynx has a useful article on bladder stones
http://www.guinealynx.info/stones.html
As long as she is eating normal quantities of food rater than just picking at it then you don;t need to use CC......however I would weigh her every day at the moment so see if she maintains/regains weight and doesn;t lose any. Pain can stop a piggie eating hence why painkillers in this situation are advised...the rimadyl etc you mention is fine if she gets diarrhoea with metacam.
Adhesion formation following surgery can occur and can impinge on gut motility....so also keep an eye on her poo output to make sure they are of normal frequency and appearance.
HTH - Good luck..
x