The girl's clothes are more expensive than the boys.
The camel is called as the ship of the dessert.
My sister said these things; are they correct? I'm wondering if the grammar is correct here.
The main problem I have with this sentence is the apostrophe mismatch. The apostrophe indicates possessive (in this case, a plural possessive), so you should write:
However, if your sister said these to you aloud, there's no way to tell where she put the apostrophes! So the error is not in what she said, but in what you transcribed.
As for where the apostrophes go, you can find out more about that here.
One problem here: the extra as. However, either of these are correct:
I've added quotation marks for clarity, but they wouldn't be required. The major issue is the way the verb phrases is called and is known work; only the latter takes the "as."
I'm afraid they are not. When you use the definite article the, it means that particular person/thing. So, in your first sentence, you are talking about that one particular girl or one particular shop's clothes. In such case, zero article (no article) can be used. Remember, if you are talking about the mass in general, the can be omitted.