There could be three separate people in the Bible named Timna, although it's possible they are all the same person.
Timna, the mother of Amalek, was a concubine of Eliphaz, who was a son of Esau, who founded the country of Edom. This Timna is mentioned in Genesis 36:12 and 1 Chronicles 1:36.
There also is a Timna listed as being the sister to a Horite named Lotan. She is mentioned in Genesis 36:22 and 1 Chronicles 1:39.
The mother of Amalek and the sister of Lotan might be the same person. If so, it's possible that Timna was a Horite who was taken captive by the Edomites during a war between the two groups.
There also is a Timna listed as being one of the chiefs of Edom, in 1 Chronicles 1:51. But this Timna could refer to a different person, perhaps a male.
The name Timna means "restraint."
Next person in the Bible: Timothy