While the 55-year-old referred directly to her 15-year-old daughter Zahara, she didn't say which of her "younger sisters" had also undergone surgery.
However, Shiloh, 13, has been photographed walking with the aid of crutches in recent days.
"I have watched my daughters care for one another. My youngest daughter studied the nurses with her sister, and then assisted the next time. I saw how all my girls so easily stopped everything and put each other first, and felt the joy of being of service to those they love," she continued, praising Vivienne, 11 for her compassion and care during the family's health crisis.
She then praised all her girls for their strength and for facing the challenges head-on.
"I also watched them their face fears with a resolute bravery. We all know that moment when no one else can help us, and all we can do is close our eyes and breathe. When only we can take the next step or breath through the pain, so we steady ourselves and do it."
The proud mum implored readers to “value girls” while emphasising that their “softness, their openness and instinct to nurture and help others, must be appreciated and not abused.”
“My wish on this day is that we value girls. Care for them. And know that the stronger they grow, the healthier they will be and the more they will give back to their family and community,” she concluded her essay.
The star also gave her three boys — Maddox, 18, Pax, 16, and Knox, 11 — a mention, writing that they’ve also helped look after their sisters and that they have been “supportive and sweet.”
According to People, Ange has been by her kids’ side for the past two months as they were in and out of the hospital.
“She’s been in her pyjamas, in the paediatric ward, by their side,” the source said.
Angelina shares her six children with her ex-husband, Brad Pitt.