My Mother Likes Pearl Jewelry

I never have a pearl necklace, because I not very like pearl actually. However, my mother likes it very much. I'm thinking to buy her as her birthday gift that fall on February. I'm not sure how much will it cost because I never buy it before, and I'm not sure what type of design wills she like too. Hmm..Maybe I just bring her to the jewelry shop and let her decide what to buy. But will that no more surprise for her? If I am the person who receive gift, I think I prefer someone to buy me something without let me know about it. That will be better.