3 is the most common, and the only one that is formally correct. She has everything that you ever wanted in the past, but you have the ability to want new things in the future, and she might not have those things. 2 can be a casual, spoken way of saying 3, but we usually wouldn't use it in writing. It could also be used if you are talking about a time period that is OVER, so the list of things you wanted cannot change. If you are an adult now, you could say: "She has everything my teenage self ever wanted/ She has everything I ever wanted when I was a teenager." For 1), we would usually change the grammar a bit: "She has everything I ever could have wanted". Here, whe doesn't just have all of the things that you ACTUALLY, TRULY wanted--whe also has all of the things that it would have been POSSIBLE for you ton want, if you had ever thought about them or imagined them. It is much stronger than 3, and as long as you make the word-order change that I recommended, it is a perfectly fine choice. If you are still confused about the difference between 1 and 2, that's completely understandable. Present perfect is a very difficult tense. The reason present perfect is so hard is that we use it for 5 different functions that are only loosely related to each other. One of the things we use it for, though, is "things that can still change". --I went there 5 times in 2021.--2021 is over, so the number 5 cannot change, so I use past tense. _ I have gone there 3 times so far in 2022. --2022 is not over, so the number 3 can still change. It is not permanently true. Tomorrow, the number might be 4, or even ten thousand. So, I use present perfect.

All 3 are correct but have different implications. 1) She has everything I could have ever wanted. (The use of 'could' here makes this sentence more hypothetical. Like: She has everything I could have possibly wanted) 2) She has everything I ever wanted. (Past simple -This is implies that you wanted what she has in the past, but not necessarily now. Perhaps you want something different. For example: She has everything I ever wanted when I was a kid). 3) She has everything I've ever wanted. (Present perfect - This implies that you wanted what she has from some time in the past until now/ you still want it. This could be like saying: She has everything I have always wanted).