Hypothyroid in Cats

My 12 year old Siamese was diagnosed with Hypothyroid a while ago. The vet prescribed a thyroid medication she appears to be feeling great. She is much more active and looks like she feels so much better. The only problem is that she lost so much weight in the time that it took us to diagnose her sickness.
   
These days she is only about 5 pounds, all of her bones are visable and the poor thing looks so fragile. We are trying different foods: chickens, rices, etc... but either she wont touch the food, throws it up, or absolutly loves it one day and then hates it the next. We are out of ideas on what to try and feed her that will help her put on more weight.
   
Any ideas would be wonderful :)

Clarification wanted: hypothyroid is an underactive thyroid, causing the cat to have a slow metabolism. Hyperthyroid is an overactive thyroid, causing the cat's system to rev into overdrive & burn too many calories. Which one is it?
   
As to suggestions:
   
1) Have you tried kitten food? It's lots higher in calories.
   
2) Have you tried both canned food & dry food? Is oine better than the other?
   
3) Are the foods you refer to commercial cat foods? If so, her condition may have made her unable to tolerate the various additives in most cat foods. Her immune system is probably not too great right now.
   
4) Does she like table food - like your chicken dinner, stews, that kind of thing?
   
If 3) OR 4): Consider making your own cat food.
   
You can make it by percentages, or surf for recipes.
   
One simple recipe I found is: 2 c. of ground or chopped chicken, cooked in a pan w/no water - 1 c. cooked brown rice - 1/4 c. grated carrots (raw). Blend it all in a blender & mix well. Add the fat that cooked off the chicken. Serve at room temperature. (You can nuke it lightly, & freeze any extra to prevent it from going bad.)
   
Also use turkey, ground beef & lamb for the meat part. Stick with brown rice, it's healthier.
   
Other things to add (gathered in my travels): Blend into the mix: Slightly cooked green beans; canned corn (not much, as it's very high in sugar); some cats really love cooked asparagus; cooked sweet potatoes/yams or canned pumpkin (very healthy) - olive oil, several tsp. per batch (good for the skin & fur).
   
Yogurt is good for cats in small amounts; flavor it with some gravy or get the fruit-flavored version (some cats really love blackberries & raspberries). If you can get it lactose-free, this is good, as cats are lactose-intolerant.
   
Since your cat needs to gain weight, I'd recommend buying chicken with the skin on & also cooking the chicken skin & blending it with the rest. Chicken skin is very high in fat, just what a skinny underweight cat needs.
   
Make sure the cat gets vitamins: I favor Vetri-Science Nu-Cat vitamins, $13 for 240 tablets, 4 tablets per day per cat. Your recovering cat can probably use 6 per day while she recovers her weight.
   
I found several recipes on this website: http://www.felinediet.net/homemade/
   
She may have a problem regulating her body heat. Skinny people are cold all the time. Buy a heated bed or pet pad for her to sleep on. They heat to 101 degrees (cat temp) & can be left on all day.
   
Helpful, I hope.

Thank you, sorry about the mix up it is Hyper. We have tried various dried and canned foods as well as cooking our own for her, she tends to lean towards chicken and tuna, we will definitly try the recipe you reccomended.
   
As far as her preference for one type of canned or dry she tends to like the canned over the dry since she's older she doesnt have all of her teeth. But a certain brand, no.
   
Thank you so much for the response and the website ref. we will make good use of it all. We are going to look into the vitamins and its funny you mentioned the heat thing. Silly kitty is always parked by our wood stove, Thank you again :)