How to reply when she says maybe next time, I'm just catching up on sleep

Read the message for what's actually there. She named a specific, normal reason and didn't apologize for it. That's a fairly neutral signal. People who are simply tired often say so and mean it. People who are less keen also say so, because sleep is the easiest excuse nobody can argue with.

What tips the read is what she does next. Does she offer an idea of her own, even a loose one like let me know when you're free? Does she use the words next time with any warmth? Or does the message end there with no hook at all? You won't know from one message, so don't build a theory on it. Your job is to keep the thread alive in a way that costs her nothing to answer.

The reply that works here is short and accepting. Match her tone, acknowledge the sleep briefly without any sympathy performance, then leave a single light opening she can pick up or ignore. The opening should be something she can say yes to in one word later, like a specific idea she could come back to once she's rested.

Keep the hook to one idea. One option is easier to respond to than a menu. The point is to make it obvious you aren't waiting on her to fix anything. If your message reads like you're fine either way, she gets to choose freely, and a free choice is the only kind that tends to come back.

Timing does most of the work here. Let a day or two pass before any further contact, and never send a second attempt the same evening. If she's tired, a few days later is a natural moment to pick things up. If she isn't interested, the silence tells you enough.

If she doesn't respond after one more light, low-pressure message about a week later, stop. Two unanswered attempts is a clear answer, and a third usually turns into something she has to deal with rather than something she'd enjoy. If she does come back with a plan, match it quickly and let the rest follow.