So...

Combo E: This attack gets Powerful:2. You must destroy face down cards in your staging area to pay this attack's powerful cost.

...so.

My question now is, is she limited to ONLY destroying her face down cards in order to pay or must she destroy at least 1 (to which the other non-Combo E will provide it) and she can discard momentum in addition to that?

Based on basic grammar, 'to' means 'in order to' in that statement. This suggests that the ability overwrites the basic Powerful rule, substituting discarding momentum with destroying face down foundations. That is how I read it. I understand how it could be read as 'destroy a face down foundation in order to spend momentum on the Powerful ability,' but that is putting a lot of words in the card's mouth.

-Tinman

Facedown foundations only, no momentum.

Stamps Ahoy