The foster's not the issue at all. As long as she's near me, she could care less about Lacey or anything else that's going on. If anything, she's jealous of my attention.
The issue is my dear old lady Lacey. For those who don't know, she's basically 85% blind (if not more) and what she can see is extremely blurry and dark (from what we can surmise). Everything beyond about 15ft away from her is pretty much invisible, but within that 15ft she can see basic blurry shapes/movement.
I'm also pretty sure that she can't hear all too well either. Before the foster came, she'd be standing by the gate waiting for me to come see her and I could call to her as I was walking down with no response from her. Then, when she finally saw my movement/heard me calling, she'd usually half startle because she had no clue that I was there even though I had been calling.
Anyway, I've been finding that while Lady - the foster - is fine with being away from Lacey, Lacey throws a fit when I take Lady away from her (Lacey's definition of a "fit" is neighing+nickering as loudly as possible, pawing, dancing around when tied, trotting/cantering around in a panicked way if she's loose, but nothing seriously bad - no pulling back/busting through things, bolting, whatever).
I can easily correct her+bring her back to me when I'm working with her and she KNOWS that that behavior is unacceptable all the time so she will stop if I really get on her case (basically, go back to her, say "AH-AH!!" and jerk on her halter if the "ah-ah" didn't work, then when I walk away she'll stay pretty calm, or at least contain herself, for 10+ minutes) but I feel absolutely terrible doing that to her when I know that all she's trying to do is find her buddy/protection.
She did similar things before the other horse came - nickering/whinnying for me, dancing around when tied, if I went out of her sight or she didn't know where I had gone.
I guess the thing is that she rightly doesn't have much confidence in herself to keep herself safe and she rightly has confidence in the other horse or me to "protect" her from dangers and so she's expressing these things in the only ways she can...
But, those behaviors could get to be dangerous for herself, and for others, and I would hate for anything to happen because she's worried, you know?
I'm thinking the answer might to just basically let her be, correct her when necessary and don't let her get out of hand but also be understanding of her condition.
She's extremely respectful of the rules, she knows what the rules are, and she tries her hardest to abide by the rules (including "NEVER move when you blanket is being put on" - that was put to the test last night, I was blanketing her and the foster was being super annoying so I had to really get on the foster's case, then when I turned back around, Lacey was still in the exact position I had left her in looking like "Please, help me out here.") so it's not like she's being disrespectful or anything, she's just worried.
And I realize that these are starting to be some of the signs that she might need to "go" sooner rather than later. Believe me when I say that when her life becomes 51% fear and 49% joy, I will have her put down immediately. Right now I think we're pretty solidly sitting at 95% joy and 5% fear so the Rainbow Bridge is not an option just yet. But I am aware that it's coming and I am assessing her being on a regular basis for changes that might signal that it's time.
That's actually part of why I got this foster. I chose a mare with Lacey's favorite color, the color of Lacey's previous longterm best friend who was put down a few years ago, so that if she does end up "going" sooner rather than later, maybe she'll get to go feeling protected by another horse who she thinks is her bestest friend of all time.
Forgive me for the novel, I just love this horse.