What to do when a girl goes quiet on you?

Before you decide anything, look at what she said last and how much effort was in it. If her final message was a question or she suggested something, the silence is more likely a logistics problem than a loss of interest. If the conversation was already thinning out, with one-word replies and no follow-up, the quiet is probably the natural end of that thread and not something you caused. Also check whether she ever started a conversation herself. Someone who initiates tends to come back. Someone who only answers may have been waiting for you to make the next move. None of this tells you for certain what's going on, but it tells you how much weight to give the gap.

Your reply here should be light enough that she can answer in two words without feeling she owes you a paragraph. Two kinds work well. One is a short follow-up that picks up a specific thread from earlier, like something she said about her week. The other is a low-stakes check-in that gives her an easy opening without making her explain herself. Both reference something real from the conversation. Skip anything that asks why she went quiet, anything that points out how long it's been, and anything that sounds like a goodbye. You're trying to make replying easy, not win an argument about it.

Once you've sent one considered message, give it a real window before doing anything else. A day or two is normal. A week isn't unusual when someone's schedule is packed. Use that time to live your life instead of watching the screen. If she does reply, match her energy and length instead of jumping straight back to where you were. If there's still nothing after your second message, let it sit and stop reaching out. A third message, or one that sounds more hurt than the last, turns a quiet thread into a clear signal you didn't mean to send. Silence after two honest tries is an answer. Accept it and move on.