*If there is so much water behind the door when Mildred opens it, there should be at least a trickle outside; the door doesn't look waterproof.
*A magnet doesn't exactly lose its draw when there's a stronger magnet. They add up. The weaker magnet is closer, and would interfere with the stronger magnet, which is, in this case, is much further. Besides, the stronger magnet is so far, it cannot provide exact movements needed to spell the name correctly.