She is the ex-girlfriend and friend of Dave.
Backstory
She used to be in a relationship with Dave, which ends with her saying that she "never wanted to see him again".
Alvin and the Chipmunks
A while later, she encountered Dave again. He invited her over to dinner to talk about the "new Dave". The next night, their dinner was ruined by Alvin trying to set the mood. After the Chipmunks became world famous, she got an assignment "covering their rise to fame." She was present at the big concert and helped Dave infiltrate. It is unclear if she was present when the theater attack occurred, but learned of the events later. She was invited over for dinner again, but Alvin caused a blackout.
Creatures encountered