Geralt first meets the Novice nun (or Novice nurse) at St. Lebioda's Hospital. She tells him about the goddess Melitele and about sacrifices of fruits, plants or flowers on Melitele's altars. Sacrifices of flowers like tulips, orchids, roses, etc... are not acceptable. Only sacrifices of fruit like grapes, blueberries, raspberries, or dried fruit are worthy.
Later in Chapter II, if Geralt speaks with her again, he can ask a sort of cryptic question to which he gets an equally cryptic reply but it does not seem to impact gameplay in any way. Finally, in Chapter V, he finds her in the Safe house, along with Vaska, Golan Vivaldi, the hermit, the resolute girl and Vetala. They speak about whether or not Ithlinne's prophecy is coming true and she also gives him an update on Carmen and Vincent.