How long should I ignore her or do I just wait for her to text me first?

Anonymous
I've been going out with this girl for quite a while now. We texted regularly and yesterday, she told me that she's going to the mall with her family. I replied and told her to have fun. She ended up didn't reply or text me for at least 6 to 7 hours. I'm not mad at her but i could see that she was still active on her whatsapp so that kinda driving me crazy as to why she didn't even bother to text me to at least tell me that she is busy with something. When she eventually texted me that night, i just replied her with short answer. And she did ask if i'm mad at her. I told her i did not. Later, I told her that i'm out with my friends and asked her to just go to sleep. That was my last text. Now i kinda regret what i did. But, at the same time i'm still mad at her for not explaining to me why didn't she text me. I pretty sure she knows that i'm angry that she didn't reply my text cause she knew that i knew she was online the entire time. Should i just let go of my ego and text her first? and say sorry?
How long should I ignore her or do I just wait for her to text me first?
3 Opinion