Thea Sprecher (played by Christine Firkins) was a deaf girl from Arizona who attended the same school as Gibson Praise. The two of them were friends and she was the only other person Praise spoke to about his alien DNA.
While the entire school was taken out of class during the FBI hunt for Praise, Sprecher left on bike to a remote location Praise and her knew about. Unbeknownst to her, Dana Scully was following her in order to find Praise. She reached the bunker and apologized to Praise when Scully arrived.
Back at the school, when the Alien Bounty Hunter tried to capture Praise, Sprecher was the only person to identify his disguise because his hand was bloody after nearly killing Agent Landau. She backed away, and so the Alien then assumed Sprecher's identity to successfully capture Praise at the MacLaren Medical Center. (TXF: "Within", "Without")