She can use the AP to reenter if it's still valid. People with recently approved green cards enter with AP all the time without a problem. At the POE they will realize she's a permanent resident and let her in (and if they don't realize it she should point it out).
She can't get an I-551 at the consulate. Perhaps they could give her a transportation letter, but if her AP is still valid they'll tell her to use the AP instead.
However, her entry would be a bit smoother if you send her the GC, so she wouldn't need to go to the secondary inspection room. But that's for the two of you balance the risk of losing the GC vs. the convenience (or lack thereof) of using AP to enter.