There is no doubt that Platinum is a better fit for her.
It didn't seem right for her to be working at Silhouette with "the golden girls" (ie. Jeannie, Samantha and Lauren). Also, Platinum is a lot like HFH - but without all the screaming between mgt and MPAs.
Regardless if Tarah joins her or not, Platinum clients are the obvious winner. In my opinion it might be best if Tarah goes to BP, because she is a classier MPA and deserves the best looking MP (which is undoubtably, BP).