Yes, you should file for an extension. If you know what the corrected W-2 numbers will be, you can determine whether you owe any taxes with your federal and state extension.
There are many W-2Cs completed every year by employers so I imagine that they have no liability. If you could not determine your estimated taxable income due to the W-2C (for your extensions) which resulted in a large penalty, you may at that point have a claim with her employer.
