Oh my, I am so touched with all your responses and ideas. I've laughed, cried and smiled at every one. I feel so sad without her and it's been really nice to talk about her here, thank you.
She always hated a fuss and could quietly turn her hand to amazing crafts without too much bother. She'd be rather bemused to see me emailing around over a thread colour. 
Thank you to @JoJothesquirrel @Muppetry76 @NoWordForFluffy @BlackberryViolet @Sewrainbow @Foxyloxy1plus1 for hunting in stashes and sharing number shades.
Thank you to @UselessTrees 
plus @sleepyhead @Pralinelatte @stayathomegardener @SoupDragon @Sewrainbow for the gold leaf finish votes. Would never have thought of that.
I have a lovely email today back from a long-term experienced crafter in the trade, who said the Anchor shades haven't really varied in colour much. Which got me thinking. My friend wasn't really much of a red fan. The embroidery instructions say scarlet 46, but she loved darker Autumnal shades and I think she just picked out a favourite instead! So no wonder I'm confused. 
I've gone back through all the threads and picked out one without a numbered wrap on it, just a sticker. Who knows whether this is actually 72, but it looks pretty close?
I'll see whether this looks 'right' and hopefully there'll be enough to finish it. She was a traditionalist and I'm not sure what she'd think to gold threads on this! I'll see how it feels as I approach the last leaf 
And yes, @LyingWitchInTheWardrobe, I like the thought of her looking down and picking over the skeins here.
I'll be back to talk about experienced Facebook Groups @SDTGisAnEvilWolefGenius if it doesn't work out. I'm rather new to sewing myself and it's quite daunting to attempt to finish her careful work.
Thanks everyone, you've given me a new energy to get to it.