Why does she take forever to reply?

I just met Sara which is my dad best friend daughter. I spent a night at her house and we had a good conversation not only that she seem into me. She was fiddling with her hair too. She added me on facebook and messaged me that night to give me the wifi password. I slept early and text her the next morning that i had unlimited data anyway. That morning she talked to me about it because i had unlimited data but i notice she hasn't read the message. When i left she packed a meal for me so i messaged her later that day to say thanks for the food. She didn't respond until a few days later saying she didn't see it. Maybe i should try getting her phone number instead of messaging app. Also i didn't show much interest in her while i was there because it'd be awkward with her father.