I think "screwing up" has an incorrect connotation that she didn't commit fraud deliberately. People who have never been anywhere near a coal mine express anger at Don Blankenship for contributing to the deaths of dozens of people via deceiving inspectors. So it doesn't seem strange that people would continue to be angry at Holmes, when everybody depends on medical services such as blood tests that they can trust. Ordinary people almost always die in circumstances that only amount to statistics and not a newsworthy outrage, but surely it is an injustice if casualties are deemed irrelevant in a situation like this.
They were making blood tests on some Walgreen stores. I'm not exactly sure if those were using their (flawed) process or faking it by using existing processes.
There labs were in the market for years, using a "mix" of their own tests and also standard tests from other manufacturers. What they could not come out with was any FDA approved test of their own except for one (for herpes).
The basic issue is that drawing a pin prick of blood from the fingers results in a lot of "interstitial" fluid. The combination of a very small sample and poor quality made it hard to create reliable tests. In reality Theranos labs were mostly taking vials of blood from veins for standard tests, instead of the pin pricks they were touting. Once this became public the bottom fell out.
Edit: The worst part of what they did was that they would take smaller samples than normal and then run them diluted on standard machines . This is because the standard machines needed a larger volume. This gave patients less reliable results than they would have had a larger sample been taken in the first place. And i think this is really unforgivable, because it has real life consequences for people.