I think it was Jasdelia at that point, right? I don't think Jasdelia liked the idea of a super-powered thief helping out the good guys opposing her plans.
Obviously at the time this came across as 'in-character' jealousy on Cordelia's part. Generally Cordelia is very protective of Angel throughout the show, especially when it comes to women with romantic/sexual designs; see Buffy, Kate Lockley, Beth the telekinetic, Darla and later Eve.
Even in Fred she saw a crush that she urged Angel to quash as soon as possible, and thereafter she didn't seem that fond of Fred.