1. It is very hard for women to build muslce, especially accidentally.

2. No matter how much you tone, you won't be able to see it unless you lose the fat underneath it. If you workout, and keep eating poorly, the muscle will just make you appear bigger overall.

3. To lose weight and gain muscle you'd have to consum less calories than you need (basically), and lift weights. Lifting weights will build muscle slightly, and once a little bit of muscle is made, it burns more calories.

^ you're assuming she needs to lose weight though..

Free weights are a great way to get toned. Unless you get into the real heavy weights, you will not bulk up to any large size. I have several sets of dumbells I use at home to keep my upper arms toned. If you stick to smaller weights and focus on repetitions, it will tone your arms nicely.

You're right, I was assuming she needed to gain weight. I just have ths mindset that if you don't work out, you can't be in the best shape possibnle. But I could be wrong... We'd need more info from her. And I do recommend weights for women, as I do them myself.

I try my best to lift the heaviest weight I can and you can't see any muscles on me

unless you take testosterone you will not build bulky muscles.
Really watch your diet though
i am a personal trainer and I have trained girls who are 14 years old so you are not too young.

Make sure to eat 6 times a day

40% carbs
30% protein and
30% fat

that's based on what you need say 1500 calories per day

Both good and bad advice given in this thread so far.

First off, you don't have to worry about becoming "muscular" in your arms so it turns guys away, in fact, having toned arms and shoulders is typically a very attractive thing.

As someone mentioned, stick to light/medium weights and focus on repetitions and sets. Don't try to lift the very heavy weights. Focus on light/medium weights, with 5-6 sets. You should be struggling and sweating for the last few sets, even though the weight is light... This is where you'll do the majority of your toning.

Eat properly, focus on proteins post workout, and simple carbs pre-workout.

This will give you those sporty but smooth (not bulky) kinda arms that help you look fit and healthy.

Justin

My opinion is to do but please do not over do.
Sincerely,
sandy