In French, you can equally say both : elle est jolie dans/avec cette robe, but "to look lovely/pretty" does not directly translate to another verb than "être".
However, the French prefer "avec cette robe", because "dans cette robe" probably refers too directly to her body shape, rather than her overall looks.
People continue to say that on these boards that "since you can say such-and-such in French, you can translate it like that into English as well." This is simply not true; since the connotations in each language are different, the accepted English phrase needs to carry the same general meaning.
If the French want to be specific and distinguish between "this" (something close by) and "that" (something far away), they can use the suffices -ci and -là respectively.
cette robe-là - "that dress"
cette robe-ci - "this dress"
Otherwise, as you have observed, they just use cette robe for either "this dress" or "that dress".
-ci comes from ici which means "here" and is also found in the demonstrative pronoun ceci (this). -là you may recognize is the word for "there", là and is in the demonstrative pronoun cela.
Note that even though cela (that) is a marriage of
ce + là i.e. "that + there",
there is no accent on the "a" in cela. Needless to say, ceci (this) is a combo of ce + ici i.e. "this + here".
These websites try to explain the difference:
I don't think either answer is correct. "With that dress" is grammatically incorrect. And saying someone is nice implies they have a good personality, which would have nothing to do with what he/she is wearing. You can say "she looks nice".... or "she is pretty....in that dress".
What would you call a watch that beautifully matches or complements a dress, if not "it"?
If you were talking about a person looking nice because of the dress she was wearing, you would not use the preposition WITH; you would use IN.
"She looks nice in that dress."
The use of WITH tells you it is something that is worn together with the dress and whatever it is, it complements the dress, hence "It is nice with that dress".
When you use "nice" to talk about a person, the sense is that you are talking about their personality. So your sentence does not convey to me that you admire how the person looks in the dress. What I understand from your sentence is that this person is normally a bad person but when she wears that dress she becomes a wonderful human being: She is nice in that dress, but once she takes it off, she turns into a horrible person.
To convey that you mean the dress suits her nicely, then you need the verb "look": She looks nice in that dress.
A nice person is not necessarily someone whose appearance is appealing to one's eyes. So saying someone is nice simply tells us that that person's temperament is good. For instance, the Beast in Beauty and the Beast was nice (had a good heart), but I would not say he looked nice.
I didn't need to but I exercised my freedom to respond to a question posted on a public forum while others ignored it (You are welcome). I even threw in a freebie: a tip of how one can avoid being redundant in the future and save time by finding answers while in the thread, instead of waiting and hoping someone cares enough to answer one's question sometime before Kingdom come. (Was a pleasure to be of assistance to you.)