Hi Pinetree
have some info - not very helpful though but explains why she can't be found, yet!!
on Ancestry.co.uk 1881 census there is a 'Mrs Smith' see ref: RG11/3081/128/2 - address: Coventry Rd, Thurlaston.
No age given and occupation given as 'out visiting' - obviously when the enumerator called she was out and he must have asked a neighbour who lived there. Don't know if you had found this out already!
I've tried searching for her as 'visitor' but can't see her under that description, I don't think so anyway. There are a few Eliz. Smiths describes as mother-in-law however, so if you have details of the men any of her daughetrs may have married that may narrow down the search.
Regards
Graham