Questions & Answers about Dann weint sie vor Freude und stimmt zu!
Why does the sentence use vor Freude instead of aus Freude?
The preposition vor is used for involuntary, physical reactions to an emotion, like crying, shaking, or blushing. Since she is spontaneously crying and can't help it, it is vor Freude. We use aus when someone makes a deliberate choice driven by a feeling, like helping someone out of love (aus Liebe).
Where is the article for Freude? Shouldn't it be vor der Freude?
When vor or aus are used to express the cause or reason for something, we drop the article before the emotion or abstract noun. This is called the zero article, so we say vor Freude rather than vor der Freude.
Why doesn't the second part of the sentence say und sie stimmt zu?
Because the subject (sie) is exactly the same for both verbs. When you connect two main clauses with und and the subject doesn't change, you can just drop the second subject to make the sentence flow better.
What is the zu at the end of the sentence doing?
It is the prefix of the separable verb zustimmen (to agree). The conjugated part (stimmt) takes the normal verb position, and the separable prefix (zu) gets kicked to the very end of its clause.