I've never seen it here in South
Africa, but it looks convincing enough. Often we find names being combined - perhaps the names of the grandmothers, blended to make a distinctive name for a granddaughter but one which still has family history built in. Examples are Louette from
Louise and
Henriette, Rialette from
Maria and Aletta, Anri from
Anna and
Maria ... you get the point.
Another possibility is that
Senta might have been expanded, or perhaps blended as above.
Senta plus
Margarita? Where did you find it?