I think you're right...I've found some suggestion that she may have remarried into the Green family (nothing remotely concrete though!).
I've found a marriage of Elizabeth Mary Beach in 1845....and I wonder if this is her remarriage.
Thanks for all your help on this, I'll try to keep you informed (plus obviously I'll update my site with details as I move this forward). I'm marking this item as Completed, to prevent others feeling the need to get involved...I think you've given me enough for me to be thinking about for a while now!
Many many thanks for your help...its hugely appreciated