In all eutherian (mammals excluding the marsupials), the female (who is $XX$ for the pair of sexual chromosomes) inactivates one of her $X$. This is called dosage compensation. This inactivation occurs at a given time during the development when randomly one $X$ is silenced. The daughters of this cell inherit the $X$-inactivation pattern epigenetically, which results in some part of a tissue having the maternal $X$ inactivated while others having the paternal $X$ inactivated (daughters of some other cell which silenced the paternal $X$). This process yield to the famous turtoiseshell coat in female cats.
Assuming X-inactivation occurred in the lineage of the oogonia/oocytes, when does the X-inactivation and X-reactivation occur in the lineage of the oocytes?
A bit developed
Are the X inactivated as well in primary oocytes? If not, is the $X$ inactivated in the secondary oocytes in a primary follicle? If not, did the diploid mother cells of the secondary oocytes have one $X$-inactivated? If yes, did all diploid mother cells of oocytes have the same $X$ inactivated (inactivation occurred relatively early in the development or is there an imprinting) or did the mother cells of oocytes differ in the $X$ they have inactivated (inactivation occurred relatively late in the development)