I think that the ponytails were just part of her seduction to get him into a better position for murder. Since she came there to murder him, I don't think that blackmail or anything other than seeing him dead was on her mind.
If she often did her hair in pigtails around him then that's one thing. If she did it this one time I think it is like another poster said...maybe she thought it would minimize her hair shedding during the time she was in the house on June 4th.