Of coarse check with USA immigration but should not be a problem since she has VISA already...My guess is that her VISA already has a date of return on it and once you present VISA to officer you can explain what happened with ticket if they ask to see...he will stamp how long the VISA is valid for...but others are correct as it depends on the officer and how much he wants to bust your balls..but the bottom line is that she has a valid VISA....
My wifey and I are now exploring Texas at a leisurely pace. US Immigration gave her 6 months. We are now spending quality time together. Hope a baby Doomas comes out of this