Rescued Siamese is pregnant

Hi everyone. Im new here, so nice to meet you! My DH and I rescued a poor pitiful Siamese female a bit ago. Don't even get me started, or I'll get angry all over again. Grrr. She was "supposedly" fixed. Well, she's now very very pregnant by the ONLY unfixed male we have. I won't say I'M not thrilled... but I HATE being lied to. As we have NO idea when the conception date is, I'm nervous. The lady who we rescued her from said she had had one litter of kittens and was a HORRIBLE mother. We found two abandoned kittens in our shed (eyes barely opened) and she adopted them without question. They are 8 months now and SO SO healthy. My questions are... she can get to dry food and water all day every day. We also give her tuna at night, which she loves. But her coat is going dull. And she's HUGE, but I can't feel any babies moving. I'm worried. Any advice for expectant momma?

Welcome to TCS!

First the obvious question - Are you sure she is pregnant - have you taken her to the vet? 

There is a uterine infection - pyometra that can mimic pregnancy in shape and timing.  It can be fatal.  If the cat is large and you don't feel kittens moving please see a vet.

If she is pregnant we have some short and sweet articles that you will find helpful.  Here are a few:
[article="29718"]Nutrition For The Mother Cat  [/article][article="31306"]How To Tell If My Cat Is Pregnant  [/article][article="31379"]Pregnant Cat What To Prepare For The Birth  [/article][article="31414"]Help My Cat Is Having Kittens  [/article]
For food we recommend kitten food.  It has extra nutrients and fat that the developing kittens and mom needs.  Wet food would be better than tuna since it has more nutrients. 

Others with more experience will be along to offer advice.  Keep using this thread for any questions or concerns you may have.

Kittens can be seen/felt the last 2-3 weeks of pregnancy. Can you post a picture of her? I agree that dry kitten chow and wet food is best during pregnancy and nursing, and will perk up her coat. Fancy Feast makes a tuna flavor wet food the cat will probably enjoy!

First off congratulations on your new babies.

Second I agree with the others a high protein kitten food is needed for the expectant mother.

Third I wouldn't keep feeding tuna. As many others on this site say it has a high mercury content which isn't good for mommy or her babies. Maybe a salmon food would be better.