Without a picture of your arms it's impossible to have a suggestion. Perhaps your friend just doesn't know what looks good?
Perhaps your friend is a bit jealous because your arms are better, more toned than hers. The real, I think more important question is, how do you feel your arms look and what are you trying to achieve? Doesn't really matter what she thinks.
I agree with Juliana. People have different opinions on muscular arms for women, but in the end, its what you think that matters most.
Perhaps your friend is jealous of your awesome progress and she doesn't have any muscles herself to show off?? When others are jealous they oftentimes say negative things to others to make them get back to their comfort level.
As far as how much weight to lift: choose a weight that will be very difficult to complete the last rep with good form. You want the amount of weight to be very challenging for the last rep(s), but not so much that you cannot complete the last few reps. It takes some trial and error to get there, but you will!
With using 10 lb. 3 sets of 12. you are not gaining muscle mass you are toning the muscle you already have. By doing this you are loosing body fat. Sounds to me like your friend might be a little jealous. Again it doesn't matter what anyone says or thinks, as long as you are happy with your progress. Stay motivated and don't let the opinions of others set you back.
If you're at the gym to please her, definitely put on some fat to cover your muscles. If you have another reason for going, you may want to put that ahead of your friend's opinion.
The question I am most concerned with when I work my upper body is whether I can lift/push/pull all the things I want to in my life (I'm moving soon--pretty good motivation at the moment).
What are your goals?
Nothing sexier than a fit buff toned female as long as its natural and not one of those freak shemale steroid types that looks and talks like a man but with big fake implants.