Translation:She wants both the red shirt and the black shirt.
I used the "either...or" version once (on another exemple) and they said I was wrong...they used the expression "be it...or" which although I can see at a right option I believe it's far from being the most utilized. Now I used that expression and they said I was wrong. I love this corrections.
I'm not sure why "would like" is in the list of definitions. In English, this is (effectively) the conditional mood for the verb "to want". The conditional mood basically expresses a hypothetical situation that may or may not hold true, and can be identified in English by the placing of the word "would" in front of the verb. For example, "I would go outside but it's too cold," or, "They would have come if they'd been invited." The phrase "would like" is similarly indicating that you would like something in the hypothetical case where you got it.
Having said all that, the conditional mood (modo condizionale) in Italian for the verb volere ("to want") in third-person singular is "vorrebbe". So if the sentence read "Lei vorrebbe sia la maglia rossa sia la maglia nera" then "She would like" would be correct. But as it is, I don't think it's right.
In natural speaking, that's exactly what an English speaker might say. However, it's not a direct translation of this sentence. I think (though I'm wondering myself) that your sentence would literally translate to "Lei vuole sia la maglia rossa e la nera" (without saying "maglia" again the second time).
Being a native English speaker myself, I have never used a sentence in that way before. When you are specifying what one is, you should specify what the other is as well. Otherwise, it could mean "She wants both the red shirt and the black (item). It could be anything. Or sometimes I would write "Both the red and black shirts."
It´s simply more long, the first one is (exaggeratedly) "rossssssa". Try this page for this "particularly differences": http://www.oddcast.com/home/demos/tts/tts_example.php?sitepal
I take my hat off to all you people who are not native english speakers! I'm finding this hard enough to learn and am a native english speaker but to have to learn all the other languages as well takes some doing. Well done all you brainy people!! I learnt german to a minor degree a few years ago - and only by living there and marrying one - and it's a long way from being perfect, and this is much more difficult, doing it on a machine with no-one to actually talk to, except occasionally my daughter-in-law who's parents are sicilian and use a lot of different words.