After losing track of Gollum, the Hobbits realized that the tunnel was blocked by her webs and she cornered them, but Frodo used the Phial of Galadriel's light to drive her off.
The tunnel was blocked by her webs. The Hobbits realized this. She cornered them. The Hobbits were losing track of Gollum. Frodo used the Phial of Galadriel's light to drive her off.