Panic over... She took a couple of panels off, fiddled around, put them back on, and it works again
Thanks for all the great advice though - I've told her that when she's allowed out again she should look round to get a feel for what she'd like when her machine finally dies. Hopefully she won't just assume now that if it's Singer it'd bound to be good.
I also discovered that the few suitable machines Amazon had in stock were grossly overpriced - e.g. up from £80 to £189