Should you message after she said she was tired and went dark?

Look at the gap, not just the last message. If she went quiet for an evening after a long day, that is ordinary and nearly always means nothing. If she has been silent for several days after a conversation that was going well, the silence is information, and the 'I'm tired' line was probably a soft way of stepping back. Check how she was texting before the tired message. Were her replies getting shorter, slower, or less curious? Did she ever start a conversation herself? People who are simply busy tend to come back with a normal, warm reply when the pressure eases. People who are cooling off often skip the reply entirely or send something polite and brief. Your read should come from the whole pattern of the exchange, and the single line about being tired is the weakest piece of evidence you have.

Also notice what the tired message did. It gave you a reason to stop without her having to say she wanted to stop. That is a face-saving exit, and it is fine to take it. Her exit does not owe you a cover story.

The next message should be simple and set no test. Do not ask why she disappeared, do not mention that she said she would talk later, and do not point out that she has not replied. Any of those turns a casual check-in into a request for an explanation. A better message is one she can answer in a few words or ignore without awkwardness, such as something you noticed or a light question about her day that does not depend on her having been online. Keep the tone the same as your earlier messages. If you were playful before, be playful. If you were low-key, stay low-key. A sudden shift to formal or serious reads as anxious. The aim is to hand her an easy door back into the conversation, not to get her to account for the silence.

If her reply comes back warm and short, match that length and let the conversation find its own pace. If it comes back flat, that tells you enough.

Send the follow-up during her normal waking hours, somewhere in the middle of a day, not late at night. A late message tends to look like it is coming from a need for reassurance, and it also gives her a reason to answer when she is least likely to be relaxed about it. Wait at least two full days after her last message before you send anything, unless there was a plan that she clearly forgot. One follow-up is fair. If she does not respond, leave it. Do not send a second message to 'check in' or a third to ask whether she got your first. Silence after one light message is her answer for now, and continuing to press will only make the conversation harder to revive later. If she eventually comes back with something warm, you can pick things up then without referring to the gap at all.