As you describe, that wouldn't be a bad starting point up from the one size fits all women's sets.  Finding a used set by Titleist is hard just because people don't resell them like the ones released yearly or more often.  A graphite lite flex is even more of a challenge.  My club doesn't take trade-ins so I usually resell my old clubs through the PGA Network.  3Balls is the usual outlet.  There are a number of e-bay retailers that have long histories of being on e-bay, thousands of sales, and guarantee authenticity.  Doing a quick search, I found about 3 sets online that were what you specified.  Interesting, did not see any 712s in graphite.  If you're willing to take the risk (beware shipments over 5 days and/or from out of the US for sure), good luck!   You'd still need to get them checked for loft, lie, and length to adjust them to her.  Because these are Titleist, there's not much savings on used 714s after shipping and adjustments and possibly re-gripping.  If she is taking lessons, maybe that shop would give you a deal on new ones to make it worth while for a full fitting and custom set.