Why is my girlfriend online so late at night?

So my girlfriend (26) and I (27) are currently doing LDR as she is away on a working vacation for a few months. We live together and have been dating for 5 years now.

However something has been concerning me lately. We chat on the phone every night and wish each other a good night and then the odd time we may send a few more texts after we hang up.

The last couple of nights though I have noticed when I reply to her texts that she sends late, she is still online. Sometimes till like 3am. At first I didn't notice but when I was seeing if she had replied and was still showing as Online then a few alarm bells started to go off. She would reply eventually but it took her forever and she was still online.

This is not like her, and I haven't said anything because i don't want to come across as accusing her of anything. What could she be up to?

Why is my girlfriend online so late at night?
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