My sister has morton neuroma. Wats that?

Nerve problem. A true morton's neuroma involves thickening and abnormality of the interdigital (b/w toes) nerve. More often, the term is used to describe a nerve irritation caused by forefoot overload which is usually related to a hypermobile first ray and tight gastrocs.
A swollen. Or a "pinched nerve" in the foot is a good way of undertsanding it.