Is this dry discharge found on the underwear after waking up a wet dream (احتلام) or another type of discharge? And must the Fajr prayer that was performed before sleeping be repeated? And does this affect the validity of the fast?

A woman experiences a wet dream just like a man. If the discharge could potentially be maniyy (seminal fluid), then ghusl (ritual bath) is obligatory. If wetness is found and there is doubt as to whether it is maniyy, ghusl is obligatory in all cases. If maniyy is found on clothing and the time of its discharge is unknown, then ghusl is obligatory, and the obligatory prayers performed after the last sleep must be repeated. Since the questioner prayed Fajr before her last sleep, she is not required to repeat the Fajr prayer. However, ghusl is obligatory for her for subsequent prayers. As for her fast, it is valid and is not affected by the wet dream or its residue.