Whilst the uniform shoulder flashes clearly show Joan's former prison as Blackmoore, the closing credits reference a misspelled "Blackmore Nurse".
When Joan is having her flashback, her uniform tag shows that she is an officer, but her uniform pips are of the governors. Joan was not the governor of Blackmoore. However, if the sequences use the same pip denomination structuring as Prisoner (1979) (and [link=tt3890836 indicates they're set in the early 1990s), then two pips would merely indicate she was at senior staff level.