Can't be. She has black hair. Trisha has brown hair.
Actually, what jjj14 wrote is true, Sloth also has the ability to shape-shift, although to a lesser extent than Envy. Specifically, when she poses as Bradley's secretary, she has Trisha's brown hair and normal looking green-ish eyes. When she reveals her true nature she shifts to black hair and the slitted purple eyes typical of a Homunculus.