Sister Ursula appeared in three episodes of Series Six of Call the Midwife. She was played by Harriet Walter.
Sister Ursula arrived to take over the running of Nonnatus House while Sister Julienne and other members of staff were in South Africa. Upon their return, Mother Jesu Emmanuel informed Sister Julienne that Sister Ursula was the new Sister-in-Charge. Almost immediately, Sister Ursula set about improving the way Nonnatus House was run by introducing a string of strict rulings which proved hugely unpopular with the other Sisters and nurses, especially Nurse Crane who learned from Sister Julienne that Sister Ursula's methods stem from her past experiences with the inefficient running of establishments. But while she may have had the best of intentions, her attempt to cut out inefficiency ultimately had catastrophic results when her new 20-minute appointment system resulted in a newborn baby almost dying from carbon monoxide poisoning. She decided to return to the Mother House after this, realizing that Nonnatus House was better off in the more capable hands of Sister Julienne.
While Sister Julienne and most of the staff from Nonnatus House are away in South Africa on a rescue mission, Sister Ursula arrives to take over running Nonnatus House, and when everyone returns, Sister Julienne is informed by Mother Jesu Emmanuel that Sister Ursula will remain in charge of Nonnatus House with Sister Julienne demoted to Deputy Sister-in-Charge, and Phyllis Crane to Nursing Sister Ursula quickly manages to upset everyone by getting rid of the television, and she also makes changes to the way the clinic is run which brings her into conflict with Shelagh Turner. Compared to Sister Julienne who ran Nonnatus House with a velvet glove, Sister Ursula takes a more iron-fisted approach and begins to make a series of new rulings that apply to the staff.
In S06E02, Sister Ursula warns the midwives and her fellow Sisters against getting too emotionally involved with their patients, but sticking to the rule proves problematic when Sisters Julienne and Sister Winifred plan to donate supplies to a couple in trouble who've just had a baby, and the husband was badly burned in a recent explosion on the docks, but Sister Ursula catches them and warns them they are nurses, not nannies. After she leaves the room, Sister Winifred says to Sister Julienne "No matter when she says, this isn't the way we do things", and Sister Julienne adds "No. It is not". Patsy also risks incurring Sister Ursula's wrath when she befriends a couple of expectant parents who are both dwarves. Fortunately the baby is delivered successfully and is normal-sized, but when Patsy returns to Nonnatus, she is confronted by Sister Ursula who says she'll have to dock her wages for defying her orders. Patsy becomes angry and puts some coins on the sideboard before telling Sister Ursula the reason she came to Nonnatus House in the first place was because she wanted to go above and beyond for her patients, to go where she was needed, and that she was now needed in Hong Kong to care for her dying father, and she departs Nonnatus House.
In S06E03, Sister Ursula continues to ruffle everyone's feathers when she announces that she is placing a new 20-minute time limit on all ante-natal, post-natal, and district check-ups in an attempt to cut out inefficiency, and when Barbara arrives late for dinner after having already had dinner with the Chen family, Sister Ursula accuses her of slacking, much to the dismay of Phyllis, who complains to Sister Julienne about the new appointment system, and Sister Julienne explains that Sister Ursula was matron of the Order's cottage hospital when it was closed down for inefficient practices, and that Sister Ursula took it very badly, blaming herself entirely. The 20-minute appointment system ultimately has disastrous results when Barbara, distracted by the time limit, fails to notice that baby Lin Chen is suffering from carbon monoxide poisoning and ends up in hospital. Not wanting her younger colleague to face any blame, Phyllis confronts Sister Ursula and helps her realize that twenty minutes is sufficient time for post-natal checks in hospital, but in district practice, they must take in the bigger picture. At this point, Sister Ursula realizes the mess she's created and that she is unfit to run Nonnatus House. After being informed by Sister Julienne that Lin Chen is going to be alright, Sister Ursula announces she is returning to the Mother House, handing the reins back to Sister Julienne, and Phyllis drives her to the train station.