Elizabeth Bear might be who you're looking for, here. In her Hammered/Scardown/Worldwired trilogy, there are at least two sets of very close female relationships that spring to mind, and those two sets also cross over with each other. Adolescent girls who deeply care about each other, middle-aged women who end up romantically involved with the same man and are friends both because of it and on their own individual terms. She writes beautifully about relationships in the middle of epic scifi.