I have an 11 week old Yorkie, cutest ever! Her name is Paris

. A week after I got her she had a Urine tract infection. Two weeks later we did an x-ray and it showed she had stone in her bladder. We just did the bile acid test and a complete blood panel and everything came back normal. What could have caused the stones??? and should i still be worried...BTW: she already passed 2 of the 3 stones that should in the x-ray. My vet is sending them to be reviewed.......thanks