What to do when she stops replying?

When she said she had to go and then said talk later, the silence is mostly ordinary. She meant it when she said she was leaving, and nothing in that message promised a reply by a certain time. The useful question is whether the conversation ended on a thread she could easily pick up or on a closed door. Look at what you sent last. If it asked her something, it is still open. If it was a flat statement or a joke that needed no answer, the ball is in your court but there is no urgency.

Also look at the time pattern. If you talked every evening and she has gone quiet on a weekday afternoon, she is probably just busy. If she never really initiated and always replied slowly, the silence may be her normal rhythm rather than a change. Different people have different reply speeds, and some reply once a day without any feeling attached to it. Judge the silence against how she usually behaves, not against your own expectations.

A message that works here is short, refers to something specific she said, and asks for an answer that takes no effort. Something that shows you were paying attention and gives her an easy opening to reply with a sentence. The job of the message is to restart the exchange with low pressure, so the reader should finish it feeling like a light nudge rather than a request for a decision.

You can tell a draft is working when she would not need to think about whether to respond. If it contains a question about her previous topic, a small observation, or a playful jab tied to something from the conversation, it is probably right. Leave out anything that mentions the silence, anything with a deadline, and any second message stacked on top of the first. One clean message does more than a sequence that reads like pressure.

After a normal goodbye, give her at least a day before following up, and longer if she said she was busy with something concrete like work or travel. Sending in the middle of the afternoon on a weekday usually lands better than evenings or late nights, because it reads as casual rather than as an eager check-in. Avoid sending the moment you finish reading her last message, since that looks like you were waiting.

If the follow-up gets no answer, leave it. One attempt is a fair effort. A second one after another day or two is acceptable only if the first got a short reply that trailed off mid-thought. If she has ignored a clean follow-up, that is your answer, and the kind thing for both of you is to stop. You can always come back later with a new reason to talk, but sending a third message into silence turns a fine conversation into something awkward to recover from.