After last night's initial meeting, I left all three of the horses out together for an hour and then went back up to put Mac in his stall per the usual dinnertime set up.
This morning, I decided to put PFP out with the boys for breakfast to see how that goes. I'm sure she'd be much happier being with them than alone in her suite, so I put all the hay out and went to her stall to get her. She was very polite, stood quietly to be haltered (not that this is anything new, but I thought if she figured she was going out with the boys she might be a little antsy), walked quietly out of the barn, and bypassed Mac to get to a pile of hay. I put her hay net out in a new location so each horse has one, and there was absolutely no drama, no squirting, no flirting, no nothing.
YAY! I don't like keeping the horses separated if I don't have to, and I think it is much better for a youngster like herself to have companionship and learn from the other horses. Mac is very clear in his leadership and tends to fly solo, so there likely won't be a lot of kissy-face interaction, but he'll do his job to protect everybody and keep them in line. She can continue to do joint back scratches with Paddy. Just letting her be with the two of them will I think be comforting for her. Plus, Mac will teach her some manners if she thinks she's all that!