How can they refer to clothes in plural when the portuguese sentence refer to cloth in singular?
A roupa (the clothing, the outfit); As roupas (the clothes).
But really, many times they are interchangeable.
In a previous task where "está" was used, only "too" before the adjective was accepted as an answer. In this case it would be "Her clothes are too tight".
I think that previous task you did might have had an error then :/ It shouldn't be "too tight" with the absence of the word "demais" which means "too much" or just "too"
Agreed. But this sentence in not in in accord with the previous one.
Is it also "Her outfit is tight"? "Outfit" was one of the given definitions.
Why is estar used here? If her clothes are tight, they are always tight, unless she loses weight.