I've been thinking it's one of the M's as well, and I've had my eye on Martine/Margriet since the beginning of the three - Marlijn just seems like she's in it for the fun of it. At this point, I've written off Martine for the mol as well - she's clearly trying to seem Mol-ish, but can't decide on a consistent strategy to do so. There's been a few instances where she's tried to play the dumb blonde, but it's not consistent enough.
With her actions this episode, I'm definitely leaning more to Margriet as the mol - she argued for the E over a comma and a dash, which needed more cars AND made the final display for the helicopter appear more like a code than an amount. During the ropes on the beach challenge, she seemed to immediately pull one of the ropes that Art called while also yelling to check with the group.