What does it mean if a girl texts you just to say goodnight?

Anonymous
I'm a friend with a girl, who has been displaying signs that she likes me, I think (kinda flirting, asking if I have a girlfriend, laughing at non-funny/lame things I say, being a little shy when it's just us). We text every couple of days, but she's never done this before: She said hi, I said hi back, then she said that she was just calling to say hello to mean and say goodnight.

I'm not sure if this means anything.
What does it mean if a girl texts you just to say goodnight?
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