Background
I have a friend, we'll call her A, who I have known for nearly 20 years now. We are both in our early 20s now. Due to transitions we have both experienced over the last several years, other people have grown close to me and I have also had the opportunity to do some traveling. A has not reacted well to this and has become increasingly more obsessive and possessive of me. (This in itself is an issue to discuss in another question.) This possessiveness manifests in a number of ways, such as telling other people that are just as important to me that she (A) is the most important person in my life and that they (my other friends) "do not matter as much". She is also putting expectations on me to consult or consider her before making any important decisions. Regardless of this, A continues to be a good friend and is an important part of my life (although I do not accept or encourage this behavior).
The Issue
I have recently graduated university and, after much consideration, A has decided that the ideal gift will be to pay for a "best friends tattoo" for the both of us. Now, I do not think this is a good idea for a number of reasons. For one, I just do not like the tattoo ideas that she is suggesting. We seem to have very different tastes in that way. Primarily though, my concern is that if I get a "best friends tattoo" with A, it will further cement in her mind that she is the most important person in my life and that I have given her carte blanche to continue acting the way she has been towards the other people in my life. I would like to simply tell A that I do not want to get the tattoo, but history has proven that turning down a perceived gift (or even telling her no in general) is likely to be taken very personally and cause an argument. I would like to avoid this.
The Question
How can I communicate to A that I do not want to get a tattoo, without upsetting her or causing an argument?
Possible Solutions
I think it may be a good idea to suggest an alternative. Perhaps a gift that is a visible recognition of our friendship without being exclusive to her and me so as not to exacerbate the obsessive and possessive tendencies that she has. If such a gift exists, I am not aware of it however, and I am also unsure how to word a request that she change the gift she wants to give to something else without offending her.
Notes
I currently have 1 tattoo, and I am interested in getting others in the relatively near future, so just claiming that I don't like tattoos or don't want another one will not work.
I am positive that this behavior is not due to romantic interest. We are both in relationships that we are happy with.
Most likely, the reason A specifically wants a tattoo is that I got a matching tattoo with my brother and now she feels jealous about that. Although if I confronted her about that, she would just claim it is because she knows I like tattoos.