Original: Mashiro first appears unnamed during episode 2 in the flower garden with Fumi when Mai Tokiha passes by and asks them as to where Mikoto Minagi scampered off to. Mashiro and Mai formally meet in episode 3, when Mashiro tells Mai that she is gathering the HiMEs to defeat Orphans.
Simplified: Mashiro first meets Mai Tokiha when Mai is trying to find Mikoto Minagi, and Mashiro is seen in a rose garden with a maid.