This is true, but also something you cannot always predict.
My youngest is named Ava. I had never heard of or met another Ava before she was born. There are many, many Ava's in her school, ballet class, etc. Ironically, her twin brother is Daniel, which I thought would be the most popular name out of all 4 of my children and there is not a single other Daniel in our school. In fact, I have yet to meet one under the age of 50 (Although I do know they exist!)
My oldest son is named Seamus. There are 4 boys named Seamus in his grade! One with the same middle name (Patrick). Another with the same last initial! (H). Never in a million years would I have guessed that one!
Our oldest DD is named Keeley. That I expected to hear when we named her, I don't. Rarely I will hear it on TV but never in everyday life and there is not another in our school district.
My point is you cannot always predict which names will be popular and which will not. Sure you can bet Elsa will be because of the movie, but if you changed it to something obscure, that name could be the next "it" name. You just never know. Bottom line, pick a name you love and that you can say over and over. If you LOVE it, then it is the right choice. Yes, know she may not be the only one with that name, but that is the case with all names.
Pick what speaks to you and what you love