No obit that I know of. My aunt(b. 1930) who is Bridget's niece, had never heard of Bridget or the fact that her grandfather was married twice.
The first time to Bridgets mother, who died giving birth and then to the grandmother she always knew, Catharine Fox.
As you said, she shows up in the 1871,1881 and 1891 cencus then just disappears around the age of twenty. Figure she likely moved away and got married but where and to who??