What is the connection between urine infection in my 4 year old daughter that is just recovering from scarlet fever?

None: Scarlet fever does not lead to urinary tract infection. One of the complications of a strep infection is, however, something called poststreptococcal glomerulonephritis. This refers to inflamation (not infection) of the kidneys after a strep infection, usually beginning 8-14 days later. It usually resolves after a few weeks, but there can be complications, so you should see your pediatrician.