Hi there
Yes, the hormones used in the Mirena device (which makes it different from other IUIs) are the concern. In some cases, they can lead to amenorrhea or lack of ovulation - which is why most clinics want donors to both have the device removed and wait a couple months before donating.
We are excited about many of this donor's qualities, so perhaps it is just a matter of reframing my expectations and trying to be patient.