This sort of thing tends to happen when there are two different theories or guesses. People merge them into one person.
The Wake theory is easily disposed of. If Isabel Wake existed, she was Baldwin's sister (daughter of Hugh and Joan), and if she married a Simon de Beauchamp, it was a later Simon, not that one.
https://groups.google.com/forum/#!topic/soc.genealogy.medieval/c4nRdGffD20