if we accept an offer does it then mean we are committed to this choice if she gets the required grades.
Well, she does enter into a contract with the universities whose offers she accepts as her firm and insurance choices, yes. However, if, on results day, she decides that she really doesn't want to go to the university which is now showing as 'Unconditional Firm' on UCAS Track, there will be an option at that point to release herself into Clearing instead.
@TizerorFizz, if you follow the link to the details on using Extra, you will find the following information about the process:
Who can use Extra?
If you included five choices on your application, have received decisions from all five, and weren’t accepted, or if you declined the offers you received, you will be able to use Extra.
The UCAS site really is a mine of information, not just an application form
.