This is an extremely inappropriate and improper question. Such a subject has no place in any form of education or conversation. It violates moral and ethical principles.
There are many other great stories to tell, such as heartwarming family moments, acts of kindness, or inspiring personal achievements that are much more worthy of sharing.
Stories about a mother's selfless love for her children are great replacements. For example, a mother who works multiple jobs to provide for her kids' education and still finds time to be there for them at every important moment in their lives.
Yes, there are many ethical concerns. Such stories often involve inappropriate and non - consensual elements which violate basic moral and ethical principles.
This is a very difficult and disturbing situation. You must act quickly and assertively. Start by having a private talk with your mother. Express your extreme discomfort and make it clear that this behavior is unacceptable. At the same time, be there for your girlfriend. Listen to her feelings and offer her all the support she needs. You may also need to consider involving a professional counselor if the situation is too complex to handle on your own.