Hi, my sisters tail lights aren't working on her dodge durango but her stop and turn lights are fine

Check the fuse first, then check the light bulbs ( some bulbs have two filaments and one will work and the other is burnt out, there's a bright one for stop and turn lights and a dimmer one for running lights, replace the bulb if either one of the filaments has burned out). Look in the owners manual for bulb # or look in the chart at the auto parts store or Walmart.

Sonds like the blbs need replaced as there are 2 elements in the bulbs trn and brakes se the same elements but driving lights /parking lights are a seperate element

Most likely a blow out tail light bulb, I know the brake lights work but there are two parts to a taillight bulb, internally there are two wires one for the brake light and one for the taillight, hope this helps, oh and make sure its the right bulb, check the manually or ask for help when you purchasing is from your local parts store.