My cat won't poop.....Please advise

I have a 13 yr old cat (female) that has just been diagnosed with hyperthyroid disease. Very treatable. The other problem is she has not gone poo. I took her in on Aug 5 for xrays, blood work and the works and she was full of poop. She received and enema and was much releived, back to her old self purring and playing. Well, she also has an enlarged heart (which could be from the thyroid thing and get a little better with the meds) and was slightly dehydrated. It is now the 12th and she still has not pooped. I call the vet every day and have tried everything she has advised. Pumpkin, hairball remidy, tuna in oil....nothing. She is hesitant to use a laxative because of the dehydration. She seems comfortable and purrs and eats and drinks so she told me to just give her time. Tomorrow will be day 8, I am a wreck. I don't want to lose my sweet baby but I don't want her to suffer but I don't know if she is. That probably sounds stupid but she acts normal or has and excellent poker face, I don't know. Has anyone experienced anything like this and what did you do? Please answer.

Try:
   
Hairball remedies (Petromalt)
   
Canned pumpkin (plain. many cats like it.)
   
Bran fiber
   
VERY EFFECTIVE:
   
1 tsp of psyllium mixed with the food at every meal until the cat poops. If the stool is very loose, just cut back the dosage until you get it right. (available at health food stores, GNC, & The Vitamin Shoppe) (I used this on an old cat years ago; it's natural & it works)
   
Feed more canned food, to put more liquids into the cat's diet. Cut back to half dry, at most.
   
The constipation can be dangerous. An impacted stool in the cat could pinch the base of the tail & cause the tail to stop working, thus causing the cat's tail to hang down permanently. This happened to one of my cats.

Thank you so much for the advice. I had tried all of that and after $400 worth of vet bills I am happy to say that my baby is doing fine. The thyroid medicine is kicking in and she is doing amazing. Her cattitude is back to her spunky naughty self, her hair looks beautiful again and she is back on her pooping schedule.
   
Now if I can just get some weight back on her and her heart to get back into shape a bit.
   
She has however learned to take total advantage of the extra attentionshe was receiving around the clock and is demanding my attention around the clock. Anything for my Coco-channell though.