I never used a Mirena, I used a copper IUD with no hormones. But I don't think the Mirena hormones would be hugely different than BCP hormones. Sometimes with BCPs you have to wait a few months for ovulation to get going again too. I think if you really like the donor you should wait for her. Especially if it is only waiting a couple of months. With some donors you have to wait anyways until they are ready to cycle because they may have school, travel plans or some other obligation.