First, thrush is usually a white spot or spots. Since your baby is so young, you may be dealing with an improper latch that is causing bruising to the baby's lips. Do you hear sucking sounds at where she is latched on? You shouldn't. After your milk lets down does her suck change and can you see that she is taking long draws instead of the shorter ones? You can usually see that at her jaw.
Just in case you did not know, here are some sings of a proper latch.
With baby held to you stomach to stomach, her nose should be pressed, not hard, against your breast, (don't worry, they flare their nostrils, just don't cover them completely)
Bottom lip should be 'flanged out' and you should see her tongue between your aereola and her bottom lip.
There should not be any squeaking, slurping or sucking noises at her mouth. If you hear like air getting through, break her latch and try again. And at this point in your nursing, it should not be hurting YOU at all. The tenderness should be gone and if it isn't, that is another sign she is not latching on right. You could always put her up there in front of your doctor to see if she is up there correctly. Hope this helped! LEt us know.