Unorthodox article placement

Solution 1:

Such and so are degree quantifiers.
Such goes before noun phrases and so goes before adjectives and adverbs; they're alternants.

Adjectives:

• She is so good [that she can make anything].
• She is so good at carpentry [that she can make anything].
• She is so good as a carpenter [that she can make anything].
• She is so good a carpenter [that she can make anything].

Noun phrases:

• She is such a carpenter [that she can make anything].
• She is such a good carpenter [that she can make anything].

Moreover, so and such comparisons usually come equipped with a that clause, to show just what the standard is for the comparison. That's their normal use.

It's also common in some idiolects to use emphasized so or such -- without a that clause -- as a general emotional intensifier, like very or extremely, but with emotional expression. This can be overdone, and is often satirized, especially when attributed to women. But this is conversational use only, not written, especially not in formal writing.

• She's so intelligent. = She's extremely intelligent (and that impresses me).
• He's such a cute little boy. = He's a very cute little boy (and I find that endearing).

Solution 2:

I am pretty sure your teacher said no such thing. The second sentence in your question is not grammatical or, at the very least, clumsy. What you can say is

Monica is so beautiful a woman that everyone looks at her whenever she walks by.

The construct X is so Y a Z is almost always accompanied by another clause, usually starting with that.

Some examples:

Herman Melville, Moby Dick:

‘Twas not so hard a task. I thought to find one stubborn, at the least; but my one cogged circle fits into all their various wheels, and they revolve.

William Shakespeare, Julius Caesar:

Caesar, now be still. I killed not thee with half so good a will.

Here, the qualifying clause is implied I killed not thee with half so good a will as I now kill myself.

The Scots Magazine, Volume IX:

Since that, the Duke of Parma besieged it in 1587, and found it, even in those days, so strong a place, that in his letters to Philip II. [sic] he complained...

Edmund Burke, The Works of Edmund Burke, Volume 2:

Nothing is so strong a tie of amity between nation and nation as correspondence in laws, customs, manners, and habits of life.