How we can know what she likes?)

Yes, surprise depends on what your sister like, and what is her age. You can be something from cosmetic products or a new decor item, new perfume, and so on

What you gifted her?

That’s why I often suggest starting with testers or discovery sets first. It gives the person an opportunity to experience how the fragrance develops on their skin <!--td {border: 1px solid #cccccc;}br {mso-data-placement:same-cell;}-->luxury fragrance and whether it truly matches their personality and style before committing to the full version. In many cases, that approach leads to a much more meaningful and confident purchase.