Ask a local weight trainer what is best for the way you lift - x/wk, lenght of workout etc. Don't be afraid of heavy weights. It takes a lot of dedication to add bulk. For some reason some women think that if they lift weights they will blow up like the michelin tire man - not that easy. Also, don't discount doing dips from your weight bench. This is a great exercise and you will feel the burn in just the right place. And, finally, your heredity does play into the shape of your arms. Sometimes you can do all the exercise in the world and your body type will dictate your success. But, keep up the great work you look great!
Respect what the Gettysburg lady said: Get trainers advice- this is just my two cents from a 30 year gym rat.
It is difficult to “add” muscle as we age. Going somewhat heavy in the beginning without straining will add or re-build muscle. Muscle memory is a real thing.
As you see and feel the muscle developing, move to higher repetitions with lower weights and keep your routine fresh with different movements to work all areas of concentration. Your diet is also very important when trying to build muscle: keep your proteins high and “bad” carbs low.
As you move through the no pain –no gain (this only applies to muscles, not joints) as mentioned by another member, in a few weeks you should start noticing results.
Best of luck.