How to reply when she just says "haha"
Verdict first
"Haha" is a polite full stop — she liked it but gave you nothing to work with. Don't explain the joke or ask if she's okay. Start a new thread or take it offline.
What it means
Usually she found it mildly funny and has nothing to add. It's not rejection, and it's not enthusiasm either. One "haha" means nothing. A chat full of them is a pattern.
What to send
Don't reply to the "haha" itself. Open something new:
Okay, serious question — beach vacation or mountain cabin?
Glad I could entertain you. Your turn: most embarrassing thing you did this year
I'll take that as a sign I'm hilarious. Now prove you are — tell me something weird about yourself
When to let it rest
If it's late or she's clearly busy, you don't have to reply at all. Let the chat breathe and come back tomorrow with something fresh.
Verdict