I think that's the main issue here. One plausible explanation for how little of opportunity was afforded her is that she just really wasn't that good of a supervisor (which begs the question, why didn't they fire her?).

Still, what here is "discrimination" and what is people just not liking her perhaps? It's very hard to tell. Regardless of whether racism plays a roll, squarespace doesn't sound like a fun place to work as a supervisor.