How to shut down flirting?

Flirting that keeps escalating usually means she is still reading your replies for signal. Each playful message is a small question: are you in? If you have been answering with enthusiasm, or even with neutral warmth, she has no reason to think otherwise. Silence and vague answers are both read as maybes, so the flirting continues.

In your head, you may have decided this is not going anywhere. She has not seen that decision. Your job is to make it visible without making it dramatic. The earlier the signal, the easier it is. Waiting for three more weeks of banter makes the eventual message feel like a betrayal.

The reply that works is the one that changes the frame. Name what has been going on in a sentence, say you are not feeling it that way, and keep the door open for friendship or nothing at all. The shape is: acknowledge that the banter has been fun, state that you see it as friendly and not romantic, and stop there. You can also just close the topic without a question at the end, which tells her there is nothing to reply to.

A draft is working if she could read it and understand that you are not pursuing this, without feeling mocked or dismissed. It fails if it contains a joke that could be read as a tease, a compliment that keeps the door open, or a question that invites her to argue for her case.

Send the message in a normal part of the day, not late at night when it reads as a loaded moment. Give it a few hours or a day if she responds with another flirty line; you do not need to reply within minutes. If she replies with a disappointed or defensive message, one short kind reply is enough, and then you can let the conversation go quiet.

If she goes silent after your message, leave it there. Sending a follow-up to check whether she is okay usually reopens the thing you were closing. You have said what you needed to say. Stop when the conversation has clearly ended, and do not come back with a new line a few days later.