In Seacole/Nightingale's days nursing was often a Lower Class woman's trade with LWC class girls working alongside, and a fair amount of prejudice towards them as little more than drunks, drug abusers and prostitutes, unless they where members of a religious order, which made them 'angels.'
One of the reasons WC and LWC girls went into service even though less well paid and harder lives, was their reputation was superficially better protected as their employers were considered responsible for their morals, unlike nursing.
Nightingale set about changing who went into nursing, hierarchies, and how they were seen, including the protection of morality, and the continuation of class and race structures.
@upsidelow your title says Lower Class girls, your post says poor or thick girls. Obviously it's all a load of rubbish, but why are you equating coming from LC as being poor or thick? I doubt most on here know what LC is any more, and expect LC to want to aspire to be 'respectable' WC to align with their values.
Plenty from LC are neither poor nor thick, but far less likely to go to uni, unlike WC or MC.
Back in the 1960's when what education and exams girls had, started to come into play; auxiliary nurses were mainly drawn from LC and WC, The LC AN's generally didn't have exams and remained AN's working hardest and being paid least. The WC girls quite often had CSE's and more choices open to them.
Registered nurses had to have O levels and tended to be MC / LMC.
Early 60's nurses were only allowed to speak to Matron or Sister when addressed by them. A standard nurse was not supposed to speak to Dr's unless Matron specifically told them to. These were the hangovers from Nightingales days.
Then shift patterns started changing to allow married women to remain in nursing. Male nurses (rather than attendants) became a thing.
Changes were made to bring SEN (state enrolled nurses) onto the register with RN's (registered nurses)
Later in 2000's it became a degree entry carer and patient care often (not always) suffered as a result.
Nowadays if you're lucky you get a well educated, smart, nurse who genuinely cares about their patient, and is allowed to look after them.
Most these days are from middle or working class, but there will always be outliers.