「問題が起きてからじゃ、遅いのよ。」
Context: It’s a conversation in a drama where a woman is trying to convince a single father to stop ignoring his health condition and to make preparations for his daughter’s future.
I know the gist of the sentence is “if you wait until a problem happens, then it’s too late” (more literally, “after a problem happens, it’s late のよ!”), but I’m really having trouble with the じゃ in the middle. Is it a contraction of a longer phrase, or is it taking the place of something?
What grammar point does this fall under?