I would go for what you want,if she's a true freind she won't be upset,she will just be delighted for you! And if yours is bigger with no additional stones it will look very different. I'm going to bore you with a little tale of mine!!!
I had a friend who always seemed envious of what ever I had, car,job,promotion,upgraded my diamond studs,new clothes etc, and as a consequence I stopped telling her about things and then started having huge guilt about keepnig things from her.It all seemed very unfair and one sided, and as I always used to make a real fuss of her and be genuinley pleased for her when good stuff happened to her it began to wear extremely thin.the crunch came when I got a 1.74 ct old cut diamond engagement ring,all she said was 'hmmm,its alright for some' she did congratulate me but that pissed me off so much that I slowly phased her out of my life.I used to miss her at first,but I now have freinds that enjoy each others good fortunes etc,so now I don't miss her at all!!!! The point to this is,I still wear a fabulous daimond ring!!! And I will for the rest of my life,I know this is a bit of an extreme example, but it just shows you never know what the future holds so go for what pleases you,its very,very sweet and thoughtful of you to be concerned like you are,but just think,she must have got an inspriation from somewhere,its just that you have got yours from her. Hope this ramble helps!!! Get what you want it really is a lifelong thing to regret if you something you don't get really want to avoid upsetting someone else!!!