I know I'm a bit late to this thread but I saw it late last night, didn't have time to respond but wanted to, and now I have some time to respond! :)
, I also have a blind horse (she's really only 85-90% blind but things would be easier if she were 100%) who was diagnosed as such last April. Her eye was swollen, she acted like she was in pain, I had the vet out, and next thing I knew, it was no longer "just" a swollen eye, it was sign that she has a disease called ERU. Prior to that, she had been somewhat blind (and I had NO idea) but that was the episode where she REALLY lost vision. Anyway, basically, I can totally understand the shock and the "What NOW?!!" you most likely have going on.
In my case, it was easier (still hard though) since I already knew Lacey prior to this incident but that's not to say that you're going to "fail" since you've only had her for a couple weeks.
Personally, I think people look at blind horses with a sort of pitying lens when really, a blind horse is "like" a blind human: they can still function really well in life, they may need more care/watching but there's absolutely no reason that they can't live happy healthy lives, post-blindness. You do have to be a bit more careful with them (keeping Lacey feeling safe is basically my #1 goal where as with a seeing horse, I would be less worried) and you have to make sure that every decision you make is the one that will build mutual trust.
I found initially that I would make choices and expect that if Lacey thought there was a better way, she'd "tell" me - however, with her limited vision (though we had had a relationship like that before) my choice was the ONLY choice for both of us. So I had to realize and accept that.
It was awkward the first few months - she'd do something, realize that she didn't know how to get herself back out of the situation, and have to wait until I came to "save" her. Or I'd ask her to do some task, she'd try her best, but we would fail because I was expecting her to just know the situation and do what I was asking and we would end up having fallen over or something else drastic because of that.
Now however, we have a deeper understanding than I ever thought possible. Basically, riding her is like becoming a centaur for a while. She's the legs/speed and I'm the eyes/brain. Being around her is like having an extension of myself that I'm not physically connected to.
I'm not really a talker so I wear my keys on a carabiner and they jingle as I walk. She's come to associate that sound as being "me" and I've found that then when I do speak, she listens pretty immediately since I'm not just streaming talk. I have words to describe her surroundings to her and we do things slowly. Fast=bad with a blind horse.
Really, I feel like having a blind horse (at least a careful blind horse - Lacey is aware that she's nearly blind and behaves as such) is infinitely easier than having a seeing one.
Don't want her to get into something? Along the fence line is a perfect hiding place (most blind horses stay away from fences since they're "hazards" - electric fence is a HUGE blind horse no-no, btw).
Don't want her to realize you're in her pasture working because she'll be "too helpful"? Take off your keys, she won't know.
Want to look like the best rider in the worllllldddd? Ride a blind horse and do cool stuff!
You don't have to be the best rider, just have a real trust connection and you WILL look like the best.
I could go on. But I would not trade Lacey for a seeing horse any day. Maybe a seeing Lacey but even so.
As far as companions go, I've found that Lacey does the best with non-horses. She loves llamas, cows, goats, sheep, etc. Basically, for her, the bodies are what matters. She always seems very stressed around horses which I assume is due to the fact that she knows the herd rules but can't see well enough to be sure she's following them.
Currently she "owns" two goats which are her favorite, by far.
And, here's a link to an article that was SO encouraging and really helpful for HOW to deal with her, when Lacey was first diagnosed. The author got her horse TJ when he was already mostly blind so she was in a similar boat as you are with Leela. He had/has ERU which is a progressive disease but the baseline points are the same for all blind horses. Blind Horse Care, Training, and Riding
Do a bunch of Googling. I googled "blind horses", "caring for blind horses", "living with blind horse", etc, REPEATEDLY and printed every interesting article to really thoroughly read. I highlighted really important care techniques and basically pretended like I was studying for a test. It's a test that'll last the lifetime of someone I love and to me, it's worth it...though it did take a while! Haha
Feel free to PM me if you have questions/just want to talk/need support from a fellow blind horse care-er, I don't want to write tooo much of a novel on your thread... Too late.
But really, pm me if you want. :)
And, in case it might make you feel better, the first ten seconds of this video features my nearly blind mare running DOWN a hill confidently - something she was barely even thinking about trotting a couple months ago (the second 10 seconds are the goats running after her which is also cute but less on topic... haha). Confidence will return, especially if your girl is still doing as well as she was initially. If you commit to being a leader for her and to being her "eyes", she will do just fine, no matter what she has to go through.
You and Leela can do it! :)
ETA- I forgot to mention that I think being a confident leader is THE MOST important thing when dealing with a seeing impaired horse. They're 20gajillion times more dangerous if they get herd bound/scared/etc. So don't fall into the "poor blind pony" trap (I did for a month or so!), it won't help either of you. Be confident, aware that she needs your guidance, and sympathetic to her needs, - be a benevolent leader.