Thank you for your query at Doctorspring.com
I understand your concern.
It is quite complex to predict about the chances. Because in most cases there are multiple factors operating along with the genetic predisposition such as obesity, usage of OCPs, multiple pregnancies, e.t.c
It also depends on couple of genes known as BRCA-1 and BRCA-2. Women with positive BRCA genes have slightly more chances of developing CA breast ( 20-25 % ).
Excluding all other factors, the likelihood of a woman developing breast ca with a positive family history in her lifetime would be between 5-15 %.
Please do not worry, those who are gentically predisposed, hypothetically if your mother was, then she should have developed the carcinoma way before the age of 89. So in her case, there must be a combination of multiple factors. So it doesn't put you on any additional risk.
Hope this was helpful,