Does she say she is a spinster? It is possible she had married before and been widowed.
More likely though that she was either illegitimate, or born from her mums first marriage, but then her mum married , or remarried as the case may be, and Laura gives her step fathers name.
When is this? Can you follow the family on censuses to see what happened?
(Dawn - you put it so much better - why do I use hundreds of words when just a few will do!!)
Welcome to Rootschat, tjh1989!