Reveal that she has turned down the other offer.
Refuse to answer the question. It is not Albert’s business.
Reveal that the other bidder has offered $400k.
Say that the other bidder has offered $550k.
At this point, there is no gain in mentioning the $400k. Albert has already offered $520k, so the $400k other offer is no longer relevant.
Pointing out that you have turned down the other offer suggests you don’t have to sell and are willing to hold out for a high price.