Is she interested or not?

So there is this girl I added on snapchat,, somebody shouted her out so we been talking for like a week now and she seems interested as she reply super fast and she ask me question as well so even before last night we were talking on text and she told me if I don't text u back it means I have fallen a sleep and Last night I called her we spoke and she goes I have to wake up 7am cuz I need to go for doctor appointment with my dad so anyways we spoke for like 15 mins on the phone and suddenly my mum called me so I hang up the call and she sent me a message saying sorry my sister is calling me and I was like okie she didn't even told me goodnight last night I told her goodnight but she left the message as open on snapchat what could this means is she interested it or not thank you