Are you asking if you should take a chance on this new girl? If that is your question I would give you a lukewarm yes. If you have used this agency before, you should have no major problems with any girl they hire. If you want to remove all doubts, wait until she gets a few more reviews. I wouldn't worry too much given the information you provided. She won't be LE. She won't be a ROB. There is no guarantee that she will be everything you are looking for, but the major risks are taken care of.

So are you asking if you should try this agency's new girl?   As previous reply, if agency is trusted & well reviewed, then there is some assurance that a new hire would be of the same caliber.  
The new girl is beginning to get reviews Which are favorable.
There is always some risk in seeing someone new but most of the risk would seem to be mitigated in these circumstances.  
It seems you are over thinking this.  If you trust the agency (as you have twice before), then I fail to understand your reluctance...  this is the one advantage of an agency.
skb