In Harry Potter, we do not see or hear about anyone conjuring more than one Patronus (that I remember), except for Professor McGonagall:
'We must alert the other Heads of House. You’d better put that Cloak back on.’
She marched towards the door, and as she did so she raised her wand. From the tip burst three silver cats with spectacle markings around their eyes. The Patronuses ran sleekly ahead, filling the spiral staircase with silvery lights, as Professor McGonagall, Harry and Luna hurried back down.
-Deathly Hallows - page 480 - Bloomsbury - chapter 30, The Sacking of Severus Snape
How is it that she was able to produce more than one?
We know that it takes a seeming amount of energy to produce one: https://scifi.stackexchange.com/a/8528/21267
Also her Patronuses (Patronii?) were small; could this have helped?