Earlier quoted context omitted.
Let's be honest (and no offense to anyone who got fired), but twitter probably had some dead weight to shed. Sadly, I'm sure some quality engineers got the ax too. Way of the world.
Quality engineers and dead weight are not exclusive. Great people who are burnt out and unmotivated become dead weight to a company. When planning layoffs, it's normal to put people who are checked out, coasting, and/or clearly planning their next move at the top of the list. That doesn't mean they are not high quality professionals.
They might have written some of the best code in a feature that management doesn't want anymore (Twitter API anyone?) but that doesn't necessarily translate in being part of those that are kept.
Maybe the dev lived in a town where they are closing the whole office and relocation is too much $$$ compared to a package. Maybe she just hasn't been with Twitter long enough to shine outside of her immediate team (who're all being cut). Maybe the folks drawing up lists had to make some concessions to keep some of their friends employed (consciously or otherwise.)