1, busy with their own things, no time to respond to your message. 2, she doesn't like you, doesn't want to have more interaction with you, and intentionally doesn't respond to your messages. 3. You're not interested in what you're talking about. 4. You offended her by saying the wrong thing.
1. No time to respond to messages
When you texted her, she was busy with her own business and didn't have time to check her phone, so she didn't notice that you sent her a message. So I'm not answering your messages, maybe I'm busy.
2. She doesn't like you
Not interested in you, not interested in your topic, not wanting to have more topics and intersections with you, is a manifestation of deliberately alienating you and keeping a distance from you. Or maybe she finds out that you like her, but doesn't want to give you hope, and deliberately doesn't respond to the messages.
3. You're not interested in what you're talking about
Your topic touches on her minefield, or your topic is so boring that she doesn't know how to pick it up, and she doesn't want to continue the conversation.
4. You said the wrong thing
What you said offended her, made her unhappy, and made her feel no need to respond to your message.