I would get my resume out there immediately, get on recruiter lists, start actively seeking a job. Network - do whatever she can to find another job, in the meantime let HR do their thing and try to hang in there as long as possible.

It's always easier to find a new job while you still have one! And then there is no explaining why you left only that you are looking for new opportunities.

I wish her the best - but I'd hang in there and be miserable until I found a new job unless the severance package was very, very good.