Is she lying to me?

This girl I’ve been talking to was acting funny with me last night. We were talking on Snapchat and when I said “i love you” she ignored that message and left me on read. She was on and off on Facebook last night but didn’t bother replying back to my message. I then messaged her on Snapchat again last night but she didn’t open it. (The second message was me asking her why she’s ignoring me)

She rang me this morning (she always does) and i asked her about this but she insisted that she didn’t ignore me. She said “she thought” she replied to my message when i said “i love you” and that her Facebook sometimes stays logged on.

Here’s my problem with that.
1) she was on and off on Facebook late last night
2) if she thought she replied to my message, surely she would have doubled checked again to see why i wasn’t replying?

I’m confused. What should I do?