Any question answered...

One solution is that I don't get the axle snug in the drop outs - if I "hang" the axle mid way in the drop outs then everything fits (just)

So, how safe, or otherwise is this? Am I likely to kill my daughter?

Otherwise. Yes. When it slips, the tyre jams against the fork locking the wheel and flipping her over onto her head. Front wheels are serious business.

I think you've bought the wrong fork, but before you decide whether to replace the fork or the tyres, first check whether the rear fits ok and whether you can make the front brake pads line up with the rim with no tyre.