The fact that they didn't would imply that the trouble of keeping her is less than the cost of firing her, which says a lot about the performance of an employee.
There is no 10x or 100x phone web-ad sales person. It's slightly more differentiable than bricklaying. You might be impressively and noticeably better than everyone else, but your greatest asset is being non-differentiable: show up on time, follow your script, go home. When you start costing more expensive people's time your marginal advantage isn't enough to save you.
I keep hearing this phrase here, often as justification for being picky when hiring. As someone who's never run a business, can someone please elaborate a bit about what it costs to fire someone? I thought, at least in the USA, there are really no worker protections. You just say "pack your stuff up and get out".