A.W.
If it's not a UTI, then you may want to consider that this is a control issue.
I see that you're SAHM. If this is your daughter's first time being away from home on a regular basis, she may feel that things around her are changing and she can't control them. What she can control is when and where she goes potty.
This could be an indication that she isn't mature enough for preschool and needs another year home with you. If you're looking to socialize her, then maybe you could join a local Mom's Club (if you don't belong to one already) and schedule play dates. Or you can put her in a ballet class once a week so she can get used to a structured, classroom enviroment.
Neither one of my girls went to preschool. I worked with both of them at home and my oldest was able to test into kindergarten early. (She missed the cut off by 5 days and it's very difficult to test in early where I live) I'm not against preschool but it really isn't neccessary.
Talk to your doctor and her teacher and I'm sure the 3 of you will be able to make the right decision.