Try wills
On Brian's site there is a burial of an Ann Shimmin in German on March 25 1827 alias Quirk.
There is also a will in 1827 for an Ann Shimmin in German on LDS film 0106245. If this is Isabella/Elizabeth's mother she should get a mention.
There are a number of potential wills for John Shimmin. Ann's will should indicate wheter John was alive at the time of her death.
Bruce