Thanks, both.
She has a National Art Pass card, so regularly catches museum exhibitions. Will double-check she knows about the free V&A tour, though!
£50 budget was just for her. We wouldn't be adding any meal/afternoon tea option, as separate dinner organised.
So it would be both of us going, with a 4hr max turnaround.
I suppose my thinking re a private tour guide who really knows their stuff was that it would provide the most bang for the buck.
Not the shopping per se (at which she's a pro), but filling in background history/offbeat, unusual stuff you wouldn't necessarily hear on a standard group tour. Perhaps being introduced to some unfamiliar small labels. But itinerary drilled down to whatever she's most interested by.
Cynical me is a bit suspicious of by how much certain tour guides' 'recommendations' are influenced by commission rates, though, so will research carefully.