Great job! Your quilting looked very nice and even. Does SIL sew or quilt? Maybe she is trying to be helpful but does not know how? Perhaps she would like you to show her how?
Anyway, I agree with everyone else. It is your quilt for your mother, you put alot of effort and love into it, do not let SIL ruin one second of the joy you had while making it. Enjoy your craft and use your talent how you see fit.
Pat in Surprise, AZ