Most of that isn't in the link you gave - your details are wrong. They're extremely exaggerated as people will see if they read that link.
Lucy Letby switched to a new mentor, who gave her a reference at the end of the placement as follows
"Ruth Sadik, a Senior Lecturer and Child Health Nurse, also provided a reference for Letby on behalf of the University of Chester. The reference referred to Letby as "competent", "committed", "amiable", "motivated" and "enthusiastic." The reference also referred to Letby as being "painfully shy" and "introverted when anxious". Ruth Sadik noted that during the university course, Letby had undertaken the following placements: four placements on general children's wards with a minimum of six weeks per placement, two neonatal placements at the Trust, health visitor/school nurse, adult nursing, an elective and ambulatory care experience and a twelve-week consolidation of practice experience. During her time at university, Letby worked as a student nurse at the Trust. Ruth Sadik highlighted that Letby's passion was in the field of neonatal nursing where clinical reports showed that she excelled and stated that she would be "a real asset to any team, especially one working in the neonatal environment when she truly comes into her own". Ruth Sadik confirmed that Letby had successfully completed her management of care delivery OSCE."
There are people who think introverts lack warmth, but that really shouldn't make us think of shyness and quietness as clues that someone may be a murderer
https://thirlwall.public-inquiry.uk/evidence/inq0017159-witness-statement-of-jane-tomkinson/, pg 16
There is absolutely no claim anywhere that a colleague stopped Lucy Letby from giving a child an overdose. Two nurses would always set up an infusion together. In this case they set it too quickly, and the senior nurse working with Lucy Letby took her full share of responsibility. Medical errors are very common in the NHS, and it's hardly surprising that Lucy Letby made two that we know of over four years of practice.