You can create a Custom Event, from the drop-down menu. You may find this quite useful, especially if you have a number of religious in your family research.
You can also create custom events for the various steps, such as Candidacy, Convent Entry, Novitiate, Temporary Vows, Permanent/Final/Perpetual Vows, for example.
You can also enter an alternate name, at Edit this person, then more options, to the right of the name.
Rather than entering Sister/Sr/Soeur, I would be inclined to use the suffix box for the designation of the order, in the alternate name. IHM, for example.
You can then choose if you want the birth name or the alternate/religious name to be the preferred name.