The buff stacks not on the same buff, but by getting new buffs. Each maiden can only give you 1 buff. I killed one, waited for it to respawn and tried it again, and it counted as THE SAME BUFF.
Therefore, your limited by the number of mobs like this there are in the game, unless you have some way to make it not a "unique" buff. If you get what im saying.
Edit: I got a total of 4 buffs just messing around with the locks that were online and it brought my 2.2 main hand down to 0.6. Pretty amazing for boss fights if you got your melee \ tanks buffed with this and summoned them.