Hmm sounds to me like she may need the cat version of a suppository, so I guess an enema? I wouldn't say emergency just yet, but I'd try to get her in today.
Idk if Miralax works same in cats and humans, but with humans it does pull water in to the stuff that's formed and...ready to go. So I'd still stay with the miralax, personally I'd increase it a bit just to get things moving. The problem is the backup just compounds itself, all the stuff behind it also gets compacted. Miralax or enema to get it all out, but still have to address the front end with something like probiotic, you mentioned pumpkin, etc. I believe problem with pumpkin (or any fiber) is that if there also isn't enough water/fluid to keep it moving, the fiber becomes a problem.
@Katherine&Ruby is the poop expert, a title I'm not sure she wants! I think she's currently trying lactulose and probiotics.