The rest of your post seems to contradict this, or at least it's a bit inconsistent. You can lose your job during or at the end of the probation period, because the probation period didn't work out, but it's very uncommon to be laid off shortly after you've passed your probation period.

I guess you mean that this is the US, so this was a kind of "probation period" for her, but in that case it should have been made very clear that she was failing.

If you lay an employee off and it's a surprise to them, you've fucked up.