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.
I'm not sure where she fits into the overall Clere puzzle either, as the line in Sinnington, Yorkshire seems to have fizzled out (though she could always bve an undocumented daughter - they weren't big on keeping track of daughters who didn't marry Important Titles), and there was another Ormesby in Norfolk which had another Clere family - connection undetermined.
I could probably help, but info is on another computer. It will be a few days. If you can sort out the line easily, go ahead. If not I can probably help, having been through the pain. I think one of these discussions at SGM was my jumping off point:
https://groups.google.com/forum/?hl=en#!searchin/soc.genealogy.medi...