So I went out with this girl once a couple weeks ago, and we had plans last weekend but she came down sick. We made tentative plans for Wednesday but she backed out saying she was still sick.

Did get a text from her this morning, just a lame joke basically but taking it as an IoI.

Now she posted on Facebook that she's going to a happy hour and wants "everyone" to come out. Now, I met this girl online but it turned out we had a bunch of mutual friends... so...

Should I put in an appearance? Worried that showing up on a Friday with so little notice could make me look needy and like I have no life. Or maybe I just show up but say I can't stay long? Or I could text her something like "looks like you're feeling better" and see if she asks me to come out?

Now this is one confusing situation but if I was in your place, I'd just act as if I suddenly bumped into her on Friday. If she's interested, stick around. But make it clear that you were on your way home and can't stick around for more than 30 minutes when you first see her.

If things go well during these 30 minutes, stay there.

But that's just me and my opinion. Others might have their different ways.

That might have worked... ended up doing something else that night though.