I Need Your Advice

I need your advice on Ribby. Until I make this decision I am stuck. I completed the armhole shaping and I ran into a dilemma. My mom requested that I make her top in medium. I am worried that if I use the length the pattern calls for on the medium size that the armholes will be too large. She has a short torso like I do. We are only 5'2". I was thinking that I would use the medium width and the small length. So what do you think? Mom you are probably reading this. What do you think? My gut says to go with the smaller length, but I would still like to hear your oppions.