The vet has suggested that a wheel from a Lego set could be glued under where the leg would be, and all will be well! So I need to get a Lego wheel that pivots so she can go round corners.
Might need to build it a little.
Probably bearing element 2x2 with rim no.2 and normal wide tyres x2 for stability, then a turn plate underneath connecting to a further 2x2 (or more depending on height needed) then glue the underside of the bottom 2x2.
Cost you about £1.16 from lego pick a brick (unless you have some lego at home you can cannibalise) + p&p