If the mummy is not currently active, I'd suggest having the pirate set it free. Basically, she finds a map or something to its tomb and sets off to raid it for treasure. The party finds out and pursues her, leading to a confrontation in the mummy's burial chamber. The mummy is awakened, and kills the pirate, the party is forced to flee as dark magical energy or whatever is unleashed, filling the tomb.

Now, the mummy's curse or whatever is unleashed and the party has to find a way to stop it. By killing the current villain, this also sets up the mummy as a credible threat. You can also bring back the pirate as an undead servant of the mummy.