Tying up in a broodmare is a big hairy deal. See below for what I would do in your shoes. Tying up can be a life-threatening disorder. I nearly lost my gelding to tying up when he was in the care of a trainer. Severe tying up can result in an abortion of the foal due to the rush of inflammatory prostaglandins due to the muscle injury and subsequent kidney injury tying up produces. I don’t mean to scare you, but this is something to get on top of rather than let it slide (the squashing of the prostaglandins, I mean… I know you were right on top of the tying up problem).
In the meantime, once you’ve sorted out the acute stage: Tying up or PSSM syndrome is a problem with how the muscles metabolize glucose. It’s a problem aside from the pregnancy. I had a gelding with tie-up and PSSM - he never had a problem with colic, it was always a huge problem with muscle spasms, charlie horses, and one episode of very severe tying up with did cause him permanent kidney damage. One time, he had a severe charlie horse in his neck, such that the muscles bulged out the side of his neck and he couldn’t turn his head. I found him in the stall with his head on the ground in sheer misery. As I massaged his head waiting for the vet, he groaned, literally, in the relief. He had one massive headache from the severe muscle clenching down the length of his neck and into his jaw. Vet injected him with all kinds of drugs and it took me a week to massage out the bulge and with shaving the hair we could see massive bruising where the muscles had actually torn. If anyone has had a charlie horse, you know how painful they are. In the huge muscles across the horse’s rump, even their ribs, shoulders and down their neck, it is sheer agony for them.
You need to make changes to the feed, specifically low NSC diet, because insulin levels/usage plays a huge role in polysaccharide storage myopathy. Check her grain very closely and start switching her over to a guaranteed low NSC grain feed - preferrably under 10%. You may have to switch her ration balancer to a guaranteed low NSC. Her hay as well must be tested low NSC. For now, I would rinse the alfalfa hay in water for 30 minutes to soak out the sugar. All you want the alfalfa for is its protein, lysine and calcium. You can do without the sugar content. Treat this very similar to Cushing’s, actually, except your fear is not laminitis, but rather chronic tying up. Keep her outside and moving as much as possible, and avoid sudden heavy exertion - in other words, if you notice her suddenly running around and being silly, go out and catch her and make her calm down, keep her walking slowly to cool out and move out the acids out of the muscles, but the moment she shows signs of tying up, stop walking her, confine in a stall, put her on flunixin (Banamine) and call your vet. You can also use Bute, but Banamine is less kidney-toxic (already a threat with tying up) and discourages prostaglandins which are produced in severe medical illness, severe injury and the like - tying up falls into this category of prostaglandin production!!
Encourage lots of water intake. My gelding also had problems utilizing electrolytes, so I always had to supplement and he was on high Vitamin E (not very much selenium at all), and I also put him on 2000 mg of Omega-3. Once I figured out all of that, he stayed pain-free for the rest of his life.
http://www.cvm.umn.edu/umec/lab/PSSM/home.html
For what it’s worth, I would have this mare on a week of Banamin (also goes by flunixin, cronyxin) about 5-10 cc, especially once you know she is drinking water really well. I would also consider a temporary boost with Regumate - talk to your vet about how to do a Regumate boost. Both these discourage prostaglandin effect and inhibit uterine contraction during an illness-related threatened abortion, which is a complication you really don’t want to endure. 
I would put her on electrolytes to encourage a ton of water drinking, especially if her urine is brown, but watch her for edema which would indicate some kidney damage or failure. I’m quite sure your vet is all over this and you would have known by now if kidney damage is severe. It is very normal after tying up to see dark brown or bloody red urine. Encouraging water to help the kidneys flush is very important. Keep her still, quiet and contained until you know the urine is running clear again. Then, let her loose into a contained paddock for another week or so and gradually reintroduce her to your herd. Always, from now on, ensure her fluid status is top rated and encourage drinking with electrolytes in her feed.
And again, reduce her total NSC in her diet. Low carb, low sugar from now on. No sugar cubes, no molasses (if you use beet pulp, which is excellent, after soaking it, then flush hot water over it a couple times through a strainer until it runs clear - this washes any extra molasses down the drain), no apples, no carrots. No treats.
Also, be encouraged - kidneys have a wonderful way of self-healing when it’s only minor damage. They can heal up to normal after small insults like this and you’d never know there was a problem. (The kidney insult comes from the muscle breakdown resulting from the damaged muscles, and those junky things float around the blood. It’s the kidneys’ job to filter all that junk out.) Your vet can monitor kidney function by blood tests measuring the creatinine. Damaged kidneys extrude a chemical called creatinine and this level goes up when there has been an insult. But like I said, most cases are minor and things heal up perfectly and the mare would never know there was ever a problem. It sounds like you caught this early and that, my dear, is EVERYTHING. {{HUGS}}
There will be some soul searching as far as rebreeding the mare though…