Malnourished

I have a 3 yr old female Siamese that enjoyed going outside. We live in a very rural area and she is fixed so an hour a day I didn't think would be bad. She went missing and was gone for 3 weeks! I searched everywhere and called to her and even asked near neighbors. I didn't find her and sadly thought a coyote might have gotten her or someone picked her up. She is beautiful. I heard her at my door today and knew immediately it was her. I let her in and she has lost sooo much weight and her eyes look bad. The inner lid partly closed. I fed her and gave her water and have her at my side. When she looks at me and meows I carry her to the food and water. Help, I can't get her in to see a vet yet and any advise is appreciated. Is there anything I can do for her that I'm not already doing?

The only thing I can think of is someone had her and she made her way home, or she was trapped somewhere.

Is she able to keep food down?  When a cat doesn't get enough to eat (one is is used to eating regularly), they can develop Hepatic Lipidosis, which can be fatal.  Are her gums yellow, or the inside of her ears?  That would be a sign.  As long as she is able to keep food down, that's a good sign.  Feed are as much as you can, high quality, high protein food.  Maybe give her some goat's milk also (but NOT cow's milk) , and add in some egg yolk to her food, raw or cooked, doesn't matter.  It's great protein and pretty high in calories. 

If her third eyelid is showing, that's not a good sign.  You really need to get her in to be seen by a Vet to be checked out.  Cat's don't show that third eyelid unless they are sick. 

She is keeping food down and I'm offering it often. The third lid shows still but there are times it is gone. She is resting a lot. I am gonna take her in Monday.

Thanks for the advise, I'm definitely gonna use the raw egg.