When your girlfriend applied for her visa she was no doubt aware that the rules are that she must apply via the consulate with juristiction for the Member State of her main destination, or if she was visiting an equal amount of time in two or more Member States then she should apply via the Consulate with juristiction for the Member State where she's spending the longest time, with evidence to support her application, so in her case she rightly applied via the Austrian Consulate.
You have now changed your plans and want to enter via Paris, plans can and do change and in all liklihood she would have no problems either boarding her flight or entering via a different country to the one she supplied evidence to support her appliction for, but she could do.
Some years ago my wife was refused a Schengen Visa because the French Visa Section had worked out that whilst we were entering via GDG we were spending a few hours longer in Italy than in France, so they regarded Italy as our main destination and refused her visa.
I don't know if we were just unlucky, she might be ok but she could have a problem.