She dressed like an owl.
She dressed as an owl.
"As" or "like"? Which one is more appropriate? My brother said that the second one is correct. He said that first one means "she dressed like an owl does."
1: She dressed like a child
The way she put her clothes on was child-like (perhaps she struggled with the buttons, etc.).
2: She dressed as a child
The particular clothing she wore was intended to make it seem that she actually was a child.
Note that in practice these are not hard-and-fast distinctions, but if forced to distinguish two different meanings, that's how most native speakers would see things. I don't suppose anyone has any idea how an owl dresses, so in OP's context the intended sense must be as per #2 above (and would normally be expressed using as).
EDIT: P. E. Dant's comment below about the simile/metaphor distinction raises an interesting point. Not that the distinction itself (simile = A is like B; metaphor = A really is B) is very important (grammarians just like it because it seems easy to understand and teach). But consider...
3: She speaks like an old woman
4: She speaks as an old woman
Where #3 looks like a simile (she's not actually an old woman; she just talks like one), but #4 looks more like a metaphor (among other things, she really is an old woman, and on this occasion her speech reflects that aspect of her identity). Also consider 1 Corinthians 13:11...
5: When I was a child ... I thought as a child: but when I became a man [I thought as a man]
...where obviously as reflects the fact that the subject really is a child or a man in each context. Thus it might seem that like = simile, as = metaphor. But that principle certainly doesn't work with the first two examples. In #1, if you saw the way she got dressed, you might (correctly) deduce she was a child, but in #2 that would mean her "disguise" had fooled you into making an incorrect assumption.
I think this is just my way of pointing out that the simile/metaphor distinction is more important to teachers than it is to students (it seems / is unhelpful in OP's context! :), but it's food for thought.
She dressed like an owl.
When looking at her (say from a distance) she vaguely resembles an owl. Maybe she is wearing a long brown frumpy gown or over-sized sweater, has very large horn-rimmed glasses, and a hairdo that makes it look like she has owl ears.
As an example of usage, often a person who is wearing a tuxedo will be described as "dressed like a penguin".
She dressed as an owl.
She is wearing an owl costume.
From Macmillan Dictionary: He went to the party dressed as a cowboy.
He dressed like an owl.
He dressed as an owl.
You can use either like or as in your sentence as a preposition; both are correct, though they convey different senses.
You use the like as a preposition followed by a noun to compare somebody or something to another. The first sentence means that he dressed like an owl does.
You cannot use the as here to convey this sense of comparison. You use the as as a preposition followed by a noun to refer to what somebody or something is or what they appear to be. So the second sentence means that he appeared to be an owl when dressed.
However, the like and as are interchangeabke when used as a conjunction to compare one thing to another:
He dresses like an owl does = He dresses as an owl does.
"Like" and "as" are much abused words even by native speakers, so no one should think there are exact rules. Usage my vary by region, economic status, or even just the "register" or fancifulness of the result the speaker wants to convey.
In general, "as" should be used when possible to compare full verbal phrases, while "like" should be used to compare noun phrases.
She dresses as an owl dresses, wearing nothing at all but the darkness of the night.
This would mean she is going around in the dark naked.
She dresses like an owl.
This would mean she somehow looks like an owl because of what she is wearing.
She dresses as an owl.
This is a special case where the "as" has a special use meaning "to be seen as," such as "She dressed as an owl at the costume party."
However, and very advanced for English, it could also be the same sense as "She dresses as an owl dresses" but with the last part dropped off for brevity (shortness). For example, "The lady of the house dresses as a servant, all alone, pulling her corset only as tight as she herself can." Notice, she is still dressed as the lady of the house, it is the act of dressing without a servant, thus "as the servants themselves do" that warrants (uses) the "as."
In addition, "she dressed as an owl" suggests that it was on a specific occasion that she owled up. On the other hand, "she dressed like an owl" suggests that she commonly appeared in the guise of an owl - it was her habit, you might say. Note that the speaker requires the listener to apply their own world knowledge to eliminate the alternative meaning ie, that she dresses the way an owl dresses, because we know owls don't dress.
For a better illustration, substitute "an owl" with "a lady".
Owls never wear dress, therefore the sentence "She dressed like an owl" has no meaningful interpretation. On the other hand, the sentence "She dressed [up] as an owl" means that she wore a costume resembling the bird. There is a difference in meaning when using "as" and "like".