Although Ursula's life differs wildly from one incarnation to the next, her older sister, Pamela, stays pretty consistent. Pammy is the thoughtful one from the get-go. Sylvie, her mother is "pleasantly surprised by [Pamela's] capacity for monotony" (6.134), which works out well for Pamela since being a housewife and mother in this time period seems to be pretty much the most monotonous thing ever.
In almost every iteration of Ursula's life, Pammy is a best friend and mentor to Ursula, is a wife to a doctor named Harold, and, despite being a relatively modern thinker, replicates Sylvie and is a mother to a ton of kids, all boys: Nigel, Andrew, Christopher, and Gerald.
Pamela is always the voice of reason, giving Ursula sage advice no matter how far apart they are, and she always does her best to take care of her sister, sending her care packages during the war. Pammy pretty much lives up to any cheesy quote about sisterhood and friendship you could embroider on a pillow.