Okay so I thought I'd finally do one of these rather than keep replying in the comments hehe
I like the idea of someone at court knowing about the spies. It would explain why Eliza had the servant seeming to stare at her at her first appearance of court, and we could have it someone high up (maybe the queen has her own little network of spies who told her about us - don't know if that will work since someone suggested the Queen). Of course it could be someone else to be the sympathiser but I figured the Queen, if she had her own network, would know when girls, who she's never heard of before, turn up at court.
Perhaps she could pull one of the girls aside for a chat, and question them about their family, then slip in that she knows their story is fabricated. We could even end a chapter there with that cliffhanger, and have the next chapter of that character start with the Queen explaining how she's on side.
In regards to Eliza, obviously James needs to (and is probably soon going to) find out about her. I like the idea that they've both been pushed to marry by various people but only seem to find someone their interested in who is forbidden by being from the other side.
I don't know how Mark wants to write James or what he has in mind, but he could at first be horribly disappointed she's a spy but swear not to tell, and then become an ally because he wishes to protect her. But if Mark has something different in mind, I'm fine with that.
If Eliza is ever to be found out at court, I think Rebecca should be the one to turn her in, or at least visit her in jail and have a good gloat. There's a rivalry growing between them - well on Rebecca's side at least. Rebecca can't stand that this newcomer gets more attention from the man she has set her sights on than her. I also think Rebecca might do subtle things to undermine Eliza (spilling punch on her, mixing up dates on invitations, telling lies to the other women of court), but not yet. She needs time to grow from dislike to hate.
I was considering writing a chapter for Sir Robert Frances but am not sure if its needed. But we could have some hints about him. I think I wrote that he was high up in the army, so he could be mentioned occasionally in that capacity. He doesn't need to be a main character, but we could mention now and again.
In regards to the ending, I think it might be interesting to have one of our girls be found out, and kept prisoner in the castle. The King might not be sure what to do with his prisoner, finding it hard to sentence a woman to death, and the Queen could try to have them freed somehow.