I don't grow rhubarb but here's what I found...

'A. Rhubarb can be transplanted in early spring or early fall (mid-September through early October). Rhubarb does best in fertile, well-drained soils and full sun. The best time to transplant rhubarb is in early spring before growth begins. Carefully dig up the plant with a spade.'

link: https://hortnews.extension.iastate.edu/2004/5-14-2004/rhubarb.html

Thanks B, guess I’ll wait until early spring - although whether I should dig the whole thing up to transplant it I don’t know. Or can I halve it and give one half to my daughter ?

Halving it won't work. It's got one main tap root. It's all or nothing with this one.

I lifted mine and it did break up into 3 crowns. I lifted mine sept 2 years ago and I planted the biggest bit where I wanted it, watered it in and left it alone and it grew a little last year but I didn't pull any. this year I took about half of it. and that's how I'll crop it in future.
the other 2 chunks went into large pots and were sold at my charity stall.

Have a look down near ground level where the stalks grow. If they come from more than one centre you can certainly split it there but if you do you'll be back to square one, having to wait another two years before you can pull any worth while amount. But I'm pretty sure it isn't big enough to split yet. You can move it in the autumn or any time when its totaly dormant and the soil and weather are fit. Its a greedy plant so make sure your new position is nice and fertile. Be careful as it has very big chunky roots (though I've never found a deep tap root)
Don't fret if you damage a root - its forgiving stuff. And don't pull too much the first year after moving (I know you...) Buy your daughter another one...

Thanks again, now I know exactly what to do with it.