You really can't spot reduce. You have to lower your overall body fat, to get arm definition.
I have VERY toned arms--unfortunately nobody knows that but me, because I need to reduce body fat. Many women do complain that their arms actually look larger after using weights to work the upper body. That is because their muscles are slightly larger, but their body fat is too high to show definition. I have been told by trainers that you need to reduce body fat to below 20% before you can really see arm definition. Now if you have low body fat and just want to work your arms--you michgt be interested in a workout called 'The power of 10" My friend is a trainer and a trainer she knows swears by it. (I also love it--and it would be great for a mom that doesn't have alot of time)
Basically you lift weights/do body sculpting exercises--very slowly--each rep is 20 seconds -10 sec up and 10 sec down. You do 8 reps until you reach muscle failure. Muscle failure means that you are so fatigued, that you cannot manage to do another rep. THe entire workout takes 20 minutes and you only do it twice a week. It takes a few tries to get the hang of it and get figured out what exercises you want to do and what weights you want to use, but there is nothing like it...
All you would need to do is buy the book. THere are several routines given in it for you to follow. I'm not affiliated with it. I just think the workout is awesome.
Good Luck | 
