Yes, she should be able to use it. I did the same thing last summer.
If I recall correctly, she can just get in line at the turnstiles per usual, and when she gets to the front of the line she'll need to let the Cast Member know that she has a WDW park hopper. They'll probably need to track down the right person, with the right machine, to verify its validity, so there can be a bit of inconvenience and delay, but not generally a big deal.