To just not understand this behaviour?

[ibetonlosingdogs]

Colleague accused me of leaving her out because me and two other colleagues went out for drinks ONCE (we’re a medium size team for reference and therefore she wasn’t the only one not invited)

I decided to do a large group lunch and invited everyone, she said she was coming and then just didn’t turn up.

Aibu to think I don’t have time for this or understand it. I don’t think you can moan, then get invited and then not turn up.

Well you should have addressed her moan the first time - what you do in our of work hours, and with whom, is your business. It wasn't a whole-team invite and you should have explained that out to her. As for accepting and then not turning up - she's obviously a flake so don't give her any more head space!