Dear William, thank you for your question. This lesson talks about using "cuando" with Presente de Subjuntivo to express future intentions. However, you can also use Presente de Indicativo to talk about facts. In your example, the fact of opening presents doesn't refer to the future but as a general event instead. It means "everytime that she opens her presents in Christmas she usually gets a perfum." Therefore we can't use Presente de Subjuntivo here, because it doesn't refer to the future. I hope it makes sense! Muchas gracias, Silvia.

Hola Nev! This difference between the indicative and the subjunctive is already mentioned in the lesson. Thanks for your contribution! Silvia