My sisters cat was diagnosed with Calcium oxide crystals & we were wondering if anyone has experience with this illness & what you did & how it worked.

Here is some info my sister sent me on Spliff:
9 yr old Female
weights 12 pounds
Calcium oxide crystals
1/4 of a can of wet food of CD hills
wet food is better because it has more water but she can eat dry food of CD hills.
cannot be treated by pills.
X ray results- has no big crystals in kidney or bladder

1/4 of a can is causing Spliff to starve greatly.. My sister upped it to 3/4 of a can & thats still not enough for poor spliff. My sister saud all Spliff does now is cries in the kitchen begging for sood. This is something Spliff has never done in the past so its greatly upsetting my sister, but shes already feeding Spliff double the food/day & is worried its going to make the crystals worse.

We both think her vet is an idiot, so this is why I'm asking here, as this is the last vet she can get too (the other one assaulted Spliff a few yrs ago & ruined the whole vet experience.. Spliff was totally cool with the vet & shots, etc.. Now shes psycho )