We are sorry to hear of the non-embryonic pregnancy.
In general, a woman who experiences a
miscarriage at least 40 days after conception enters the halachic status of
tumat leidah (similar to a woman who gave birth). If the gender of the fetus was unknown, or known to be female, she would need to wait at least 14 days before immersing. But in this case, because there was no fetus, your wife does not have
tumat leidah. She is permitted to immerse as after a normal cycle.
Please write back with any further questions.