Great to hear about your great niece loving to grow veg.
Its only worth growing if she and her family like to eat it but here are a few: -
Winter Lettuce, Winter Spring Onions, Winter Onions, Early Peas like Meteor (Sow ASAP).
Better With Fine Netted Protection: -
Perpetual Spinach, Rainbow Chard, Beetroot, Pak Choi, Rocket, Baby Spinach
Needs Fine Netted Protection: -
Radish, Spring Cabbage. Kale, Italian Kale, Turnips
With Cloche If Possible: -
Broad Beans In November (Aquadulce Claudia or The Sutton)