"She is my ideal woman."
Translation:C'est ma femme idéale.
When there is an article or possessive in front of the noun, you have to use "c'est". See the link posted below by tusharbajaj, and look at unmodified vs modified nouns.
I would also like ot know why "elle est ma femme idéale" would not be acceptable.
To those who rely on translation websites, my advice is: don't. They are wrong almost as often as they are right. It is better to use sites such as french.about.com to learn the grammatical rules. Also, you can't apply the logic of one language to another. Il est and elle est can both mean it is, and c'est can mean he is or she is, but there are rules.