Obviously, more than likely this is a peek into her future behaviour once hired. You hiring her after two no shows lets her know she can keep doing this and probably always get "one more chance".
The real question is how flaky will she be?
Calling in sick or whatever every other week but still pulling a great sales volume may well be acceptable to you.
If you feel that she has well above average potential give her another chance. Half the people that show up on time and do a perfect acting job at the interview will turn out to be disappointments down the line anyhow when the "real" them comes out.
