Talk

OK just asked DS1

Use water or a bucket filled with water & put it in the lava then it turns to obsidian, if in Survival then 3 iron makes a bucket. You can mine obsidian with a diamond pickaxe only.

That's the tide, it drags you wherever its going, either get rid of the lava already there or add more lava until it goes still.

If the game was saved before the lava came then she should be able to get onto a lava'd world as it was before the lava. If it was saved once the lava was there then it has to be built again.

Apparently

Okay - thanks. It makes absolutely no sense to me, but hopefully will to her! Really appreciate you and your DS taking the time to answer.
Thanks!

When you say "it moves her about" do you mean the lava moves her when she's in it or the game randomly puts her in different places?

apparently it makes her dig down and walk away from her world and she can't turn round / come back. Does that make any sense?

It does make sense but I'm not sure why it would happen, one button or control will move her and another will make her dig.
I would guess that she is accidentally pushing buttons which are moving her or maybe they are getting stuck.
Check the options and controls and see which buttons do what.
With the problem of lava appearing I would check she is playing in a offline world and make sure she isn't playing on a server.

Thanks - maybe it's a problem with her hudl? She's remarkably competent (unlike her mother!) so doubt she's doing it accidentally. Will also check about the server thing.
Really appreciate you offering suggestions.