This is the 94th most frequent Icelandic word.
bara
Only; just; simply.
The word "bara" is used here to indicate exclusivity or restriction—only water is wanted.
Ég vil bara vatn.
I just want water.
In this case, 'bara' conveys simplicity or restriction, suggesting that she is at home and not engaging in any particular activity.
Hún er bara heima.
She is just at home.
'Bara' here is used to emphasize that it is only or merely funny, giving a sense of simplicity or minimizing other interpretations.