When someone calls you out there's only one thing to do...... stick to your story. Possibly embellish it further if the opportunity arose.

"If that is what you need to believe in order to cope with your own loss..." Not that her intention was to rub it in.

"As high-level mage I'm always in high demand. I've received so many summons from nations far and wide that I simply can't keep track of them all. That's... really what I'm doing here now. I suppose you've heard all about the perils that are facing this land already?"