Fiona will be given a replacement hormone that mimics a female reproductive hormone that will prepare her uterus for implantation. What does this hormone mimic?

Considering that this hormone mimics oestrogen,

Explanation:

Oestrogen is going to thicken the lining of the endometrium by enriching it with blood vessels (arterioles and venules) and with spiral glands. All of this readies the uterus for implantation and later, for placenta formation.

Fiona might also be given progesterone to maintain her endometrium's lining and to avoid miscarriage.