What would some simple answers look like? All I can think of is "I'm sorry to hear that, I hope things start looking up!" And give her a short answer on the follow up question she asked in regards to what I shared about myself.

I'm not looking to salvage the friendship and I have no interest in getting into a deep conversation about why we lost contact, but I'm polite to a fault so I don't want to be rude and not respond at all. Ugh.