Then her life is arguably more valuable than the child because it means more to you. But I assume that what you are trying to say is that you don't believe in inherent value, it is the existing relationship you have with your mother that has created an acquired value that does not exist within the child.
There is an alternative. You can let the minute pass and allow all three of you to die. Then you won't have the problem of feeling guilty.
In fact you shouldn't feel guilty. You would be saving someone: you. But I assume 'save anyone' means saving another individual aside from yourself.
If you are willing, you may want to proceed with this final installment.
Now, instead of two rooms, a third room is opened behind you. In the two original rooms sits a middle-aged medical scientist to your right, and an 18 year old adolescent (you may assign the sexes of both people) who, like you, is applying for medicine. In the third room is an individual (you may not assign the identity). This individual is not strapped to any chair and cannot be killed under your command. You have absolutely no connection with any of these three people.
The rules go back to the beginning. You must decide between the scientist and the adolescent who to save. Whichever button you press will be the one you electrocute. However, you will also be electrocuted regardless of who you pick. If the minute passes, all four rooms will be poisoned.
But you are now presented with an alternative. You may withdraw from the process. If you do this, the individual in the third room will take your responsibility. However, this individual can either kill one, or kill both, but not save both and regardless will be electrocuted. Either way you will be free along with the person that may be saved.
So... are you willing to die for someone? Or do you trust the individual in the room behind you to spare their lives instead?
Considering your idea of inherent and acquired value, I'm curious of your answer.