more about bedmaids and ladies-in-waiting
@sixth-light replied to your post “hi! I just went on to Elinor Tyrell’s asoiaf page and it describes her as being Margaery’s ‘pillow friend’...”
IIRC, sharing beds with same-gender companions was very common and unexceptionable back when beds were very expensive items of furniture, at all levels of society.
That is true, for both men and women, not just because of expensive beds and housing, but also prior to the guaranteed warmth of central heating. (Which isn’t to say that some of these bed-sharers didn’t have same-sex relationships, but nevertheless most were platonic.)
Here, I am influenced by my studying of Much Ado about Nothing where Beatrice and Hero (cousins) are referred to as “bedfellows”. (4.1). Here, Hero is the lord’s daughter and Beatrice the more minor cousin whose prominence as her uncle’s ward is increased through her relationship and closeness to her cousin.
Elinor, by being close in age with Margaery, can use this closeness to make a match at court in exchange for providing evidence of her lady’s chastity in the event of scandal, something both Elinor and Beatrice cannot do in the end.
Ah yes, and GRRM is often inspired by Shakespeare’s depictions of history more than by history itself, so this is very probably a deliberate parallel. “Bedfellow” is frequently used in Shakespeare (notably “strange bedfellows”, from The Tempest)... does it predate him? Yes, my OED dates it to 1478.
But did ladies-in-waiting ever serve as bedfellows? I was under the impression that they often shared a room with their mistress, but not a bed... but a quick google check tells me that Mary, Queen of Scots, had a cousin and lady-in-waiting, Mary Fleming, who she took as her bedfellow when she was too nervous to sleep alone. Queen Elizabeth I also had several bedfellows:
In her Bedchamber, Elizabeth could de-robe, take off her make-up and withdraw from the hustle-bustle of the court. Here she was waited upon by her ladies who had the most intimate access to the Queen, attending on her as she dressed, ate, bathed, toileted and slept. Elizabeth was never alone and in or adjacent to her bed she also had a sleeping companion – a trusted bedfellow – with whom she might gossip, share dreams and nightmares, and seek counsel. [...] Sharing a bed with a sleeping companion of the same sex was a common practice at the time, providing warmth, comfort and security; but being the Queen of England's bedfellow was a position of the greatest trust, bringing close and intimate access to Elizabeth.
--Elizabeth's Bedfellows: An Intimate History of the Queen's Court
So yes, GRRM is definitely basing Margaery’s, Cersei’s, and other Westeros noblewomen’s “bedmaids” on an established role for ladies-in-waiting from our world. Glad that’s settled. :)