It shows how far she’s come from the beginning of the season in terms of growing up, becoming a woman.
For someone of Bree’s age, I think it shows such strength of her character that she’s sort of surrounded by, not strangers, but people she doesn’t really know. She doesn’t really know Jocasta that well, and Lizzie is relatively new.
It also then gives her that moment, just her and Jemmy, when she feels she might not be able to accept him.
Then that sort of motherly love comes out of her and she realizes that she can accept this baby no matter who the father is.