Search the Wisconsin Vital Records index herehttp://www.wisconsinhistory.org/vitalrecords/
There is a Laura St George who died December 13, 1890 in Chippewa County, which is where Peter died. It says her maiden name was Haverlin. There is also a marriage for a Peter St George, to a Laura Biss - don't know how that fits in. Don't put the period in after st, or you won't get any results.