I read on here that you can pull that screen to check it without draining the oil as long as she's on her side stand...

Just did that to check the screen for coolant and it pissed oil all over the floor.
I had run the bike 20 mins previously so I'd have though all the oil would be back in the tank - is this normal?

Ouch, that had to be a fun mess to clean up.

Whenever I work on the bike without draining the oil I use a motocross stand and let the bike rest on the crash bung or the bars.

Hopefully all the oil is not in the tank, if it was all the stuff that needs to be in oil would be dried and hence seized.

How much did she 'gush'?

Hard to say, she'd made about a 30cm puddle on my unsealed concrete garage floor before I'd got the bolts back in lol.

Not really worried about the oil loss as I'm going to change it soon anyway, not worried about the floor either as it's not the first time I've done that, and won't be the last. .

But anyway, I read on here that it would be ok to pull that screen without loosing oil so I was taken by surprised when the oil came gushing out.

You have to bear in mind Rich that the oil screen is considerably lower on the bike than the oil tank, and despite most of the oil being contained within the tank there will still be plenty in the filter, sump, oil pump and oil-pipes. Undo part of the system containment at a low level and it's going one way, as you found. Gravity does that.....