How do I reply to hahahah?

The hahahah is her telling you the last thing landed, or that she wants to be polite and move on. Stretched letters usually mean real amusement. A short hah or haha with nothing else can mean she's ready to wrap up. Look at what came before. If you made a joke, she's responding to the joke. If you said something personal, the laugh may be covering a moment she wasn't sure how to answer. Either way she hasn't handed you a topic, so the work is to hand her one. Think of it as keeping a door open, not walking through it for her. A reply that acknowledges her laugh briefly and then adds something new reads as easy and confident. A reply that dwells on the joke reads as anxious, because it asks her to keep reacting to a bit that's already been delivered.

The first shape is a light follow-up that adds a small detail to the joke, so she can build on it. Keep it short and assume she got the point. The second is a question about her, specific enough to be easy to answer. Something about her plans, her weekend, or a thing she mentioned earlier works better than a broad question about her day. The third is a clean pivot to a new topic. It signals you're comfortable and not hanging on her reaction. You can tell a draft is working if it's short, doesn't restate the joke, and gives her one obvious thing to say next. Leave out apologies. Leave out anything that asks her to confirm she's still interested. Skip any second joke stacked on the first. Each shape should end on something she can respond to in a few seconds.

Send your reply when you'd be happy for it to be read at a normal hour. A reply sent late at night, or in the first minute after she laughs, can read as eager. Waiting too long can make the thread feel dead. A reasonable window is somewhere between a few minutes and an hour during the day, depending on how active the conversation has been. If she replies with another laugh or a short message, you can keep going for a bit, but match her pace rather than speeding up. If she doesn't reply to your reply, leave it alone for a full day before sending anything else. Then make the next message about something new, not a check on whether she's still there. If two of your messages go unanswered in a row, stop and let her come back to you. Pushing past that point turns a casual thread into a chase, and that usually ends the conversation for good.