While it's possible that Sheridan could have easily found the hospital scrubs, it's unlikely she would have been able to get the wig to disguise herself with so quickly.
Vincent Clarkson: Coast is clear, lover boy, you can come out of the closet. Oops, I mean bathroom.
Sheridan Boothe (to unconscious Luis): I have to admit, I've done some things I'm ashamed of. I just get so angry ... I never used to be like that. I do it out of love. I do it because I want to protect you. You're everything to me, you're my life. Everything stems from you.