Aenar and Caitan aren't C-store BOFFs. You buy a token for them in the C-store, but they're obtainable from the BOFF vendor on ESD for that token, not the C-store. You can also put the tokens or BOFFs up for sale on the exchange.

Since the Borg BOFF was a pre-order exclusive and infinitely reclaimable by people with that pre-order, she's bound to any claiming character.