Hún vill hafa sitt eigið borð þegar hún vinnur heima.

Sitt is the reflexive possessive form, used when the owner is the subject of the same clause.

Here, the subject is hún = she, and the table/desk belongs to that same person, so Icelandic uses sitt.

• Hún vill hafa sitt eigið borð = she wants to have her own desk/table
• If you used hennar, it would usually mean another woman’s, not the subject’s own

This is one of the most important differences from English, because English uses her for both meanings, but Icelandic often separates them.

Yes, together they make the idea stronger and more natural: her own.

• sitt = her own / one’s own, in a reflexive possessive sense
• eigið = own

So sitt eigið borð is a very natural way to say her own desk/table.

You may also hear simpler expressions in other contexts, but this double structure is common when Icelandic wants to emphasize personal ownership.