Should you message her if she hasn't opened your last text?

Look at the whole thread before you decide what the silence means. Has she opened your earlier messages and replied to them? If so, a single unopened text is probably just timing. Phones bury previews, people skim notifications at work, and a lot of people only open a thread when they have a reason to reply properly. If instead she has never replied to a message you sent, or her last reply was short and noncommittal, the unopened text fits a conversation she's already mentally filed as low priority. Neither reading tells you for sure. What it does tell you is how much weight to give the silence. A few days with no open after a warm exchange isn't much. A few days with no open after a conversation that had already gone flat is a clearer answer.

Also check how long you've been talking. Two days into an app match gives you a lot of room. Three weeks of regular texting and a stalled thread is a different situation, and it usually means something has shifted on her end.

The best next message is one she can answer in a sentence without re-reading the whole history. Refer to something concrete, like the taco place, the film you were discussing, or the plan you floated. Keep the ask small. A question with an easy yes or no works better than an open invitation she has to think about. Avoid anything that makes the non-reply feel like a problem she has to solve, like asking whether she got your message or saying you thought she might have forgotten. Those lines put her on the spot. A light, self-contained message lets her reply the same easygoing way she would have if the first text had landed on a good day. The silence should be easy for her to leave alone and easy for her to break.

Timing matters more than most people expect. Sending a follow-up late at night, or on a weekend evening when she's probably out, can come across as either hurried or like you've been thinking about it all day. Pick a normal part of her day, usually mid-afternoon or early evening on a weekday. Then wait. If she hasn't replied to a follow-up within a couple of days, leave it. One follow-up is a reasonable amount of effort after a missed message. Two is pushing it, and three is a message she'll feel obligated to answer or will avoid. If the thread stays silent after your follow-up, drop it for now. You can always pick it up later with a fresh reason to message. Stopping there isn't giving up. It's letting the silence answer the question.