I'm not big on texting, because most communication is non verbal so you can't convey the Same message texting as speaking, but it's a part of the world

we made a joke how her manager left so now she can drink the margarita mix they sell since they dont sell alcohol. So the message is along the lines of "I'm going to bed, but hopefully you aren't too hungover tomorrow from the margarita mix." The purpose of this is to make her decide if she wants to answer, since you said you are leaving while at the same time gave her something she can respond to. It can make the girl think If the better option is to not answer, or to answer. Then she is gaming you.

Why let her know anything you are doing?

Women love mystery and it shows some lack of interest, but texting back or randomly will show some interest right there.

You don't have to let her know what you are doing or when you are doing it unless you want to.

So unless you are getting into a real big conversation with a lot of things where you are talking a lot and texting back is a given I would advise against letting her know you are going to bed at all.

You could be doing this to build some kind of comfort like DW-Heart-Charmer said it sounds like you are playing the boyfriend role or someone who is pretty close to this person.

I would hope that you start seeing the world of texting as posts or as comments made on YouTube or even here where it's not that they are telling you everything that they are doing and messaging back is not a given.

It can be conversations other times it is just replying or commenting.

Best luck man.