friendship advice please?

No , you shouldn't feel so stupid... It is not your fault that the other person is not worthy of you friendship... I think you should try and find a more honest and true friend .... good luck :)

I agree, obviously your friend didn't value your friendship for what it truly was. Unfortunately that is a mistake many people go through, and yes you are hurt, angry, a little confused maybe and your trust in people will have gone down hill, but i think the best way to deal with this is ignore it. Confrontation could turn ugly and you could end up loosing a lot more then a friend and a drawing.
From this moment on if you do artwork for any other friend you must request they ask your permission before duplicating it and giving it away to others, and also, make sure you sign it somewhere so people know it is your work.
You will make a lot more friends in the years to come, true and honest friends who will remain with you for the rest of you life sharing your ups and downs and never taking your for granted, those are the friends you should cherish and it may turn out you'll be an old lady before you find that friend, but at least you'd have lived your life instead of wallowing on one bad friend.
You shouldn't feel stupid, we all get duped from time to time. It is that friends loss in my opinion. She has thrown a good friend away.

You should not feel stupid that person was not taking consideration to ur feelings. if that drawing was made from ur heart and they new that and did that to u then forget them. You deserve way better dont let that bring u down. You need to find friends who will treat u with respect and care for ur feelings.

by law she has no right to make copies of something that you gave her unless you have given her your permission to do so, but she is your friend, i do hope you had signed it and dated it, so all know of its origin, all great masters have learnt of this the hard way, i do hope she is a friend still, for she was proud of the drawing from your heart and wanted to share it with those that have no idea of your heart content, be proud. but sign and date, and maybe you might be able to make some money in the future, from those masterpeices hidden and locked away within yourself. some times its good to share a bit of yourself with others, for they will see the real you, proud, colourful, almost perfect. stand proud, but talk to your friend;-]