I just see it as her playing smart with the few cards she has got up her sleeve.
For what it's worth, I believe both acts would be relative sexual cakewalks for a girl like Bree (so I don't think she's 'putting them off' or 'afraid' by any stretch of the imagination), but the reality is that if you want Bree's first DP or Blowbang, then it's gonna cost you...you also know that because of the cost that there is an increased likelihood that few of your competitors will have a similar scene of Bree to compete with yours.
Thus, like Stella Artois, a Bree Olsen level-upping exclusive is '
reassuringly expensive'.

(See also: Ried, Amy, Limited (yet highly lucrative) anal scenes thereof.

)
Of course, if a girl was asking such inflated sums to do her first interracial scene, then it would unquestionably make her a racist bitch...at least in the mind of the IR fanboy contingent.