Moiraine tells that "events must play out in certain ways, whatever the costs."
Apparently Moiraine saw that this attack is, what she has to do. It obviously also fits with the Prophecies that Mat has to sacrifice his eye, because that would only happen if Moiraine is captured in Finnland.

Besides, I think the fact that Moiraine mentions costs and suppresses a bubble of hope (since this would be luxury), does speak against the idea that she actually knew that she would gain considerable OP strength and very well could be rescued. IMO, it was a big sacrifice by Moiraine; likely she sacrificed her ability to OP.