The correct is "Ela gosta deste café" (deste instead of desde - desde = since). So, the reason for your question is that in portuguese we use the preposition " de" with the verb like (gosto). Eu gosto "de" café. In this case you are also adding the "this" - Eu gosto "de" este café... Anyway, this is the reason: some verbs in portuguese require the use of preposition (they are called "verbo transitivo indireto") and "gostar" is one of them.