Breakdown of Ей нужно было выплакаться, чтобы снять напряжение.
она
she / it (for a feminine noun)
быть
to be
нужно
it is necessary
чтобы
in order to
Questions & Answers about Ей нужно было выплакаться, чтобы снять напряжение.
How do the prefix вы- and postfix -ся change the verb плакать here?
The base verb плакать means to cry. Adding the prefix вы- and the postfix -ся creates a specific type of action (an Aktionsart) meaning to do something to the point of complete saturation or exhaustion. In this case, выплакаться means to cry until you have no tears left, or to have a good cry.
Why is the sentence structured as Ей нужно было instead of using a standard subject like Она?
This is an impersonal construction. Instead of saying she needed something, Russian phrasing literally translates to to her it was necessary. The logical subject takes the dative case (Ей), and because it happened in the past, we use the neuter past tense было alongside the adverb нужно.
Why is the infinitive снять used after чтобы instead of a past tense verb?
You use чтобы followed by an infinitive to express purpose (in order to) when the logical subject of both actions is the same person. Even though the first half of the sentence is grammatically impersonal, she (ей) is the one who needs to cry, and she is also the one who will relieve the tension.
Does the verb снять always mean to relieve?