It looks as though there may possibly have been two of her after all. It has been rather a puzzle what the de Clare family of Wales and Gloucester could have been doing in Yorkshire, and how she could have been married to Nigel de Plumpton of that County, when she had also been asked for in marriage by Robert de Guines.
Well, it seems there was a family de CLERE, unrelated to the de CLARES, in Ormesby, Yorkshire, who could much more plausibly have provided an Alice/Avice/Amice to marry this Nigel de Plumpton person.
This could be a royal mess to clean up.