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As you can see in my previous post above, Girona stats are impressive when away but that doesnt guarantee anything when they have to face Barca in their home.
From 11 games at home (all competitions), Barca won 10 of them and only lost to Madrid.

This match will not end in a draw, and Barca will be the winner.
Interesting fact: From 15 games in the LaLiga, Barca and Girona have lost only once. Yeah Madrid beat them.
Both teams should be considered equally strong in that match, but you are right that Barcelona has a big advantage over Girona. Barcelona is playing at home and they have a good record there, but Girona did not come to lose even though in the end they could have lost. Losing to Barcelona is also not the end of Girona's struggles this season, that's because Girona will rise and make more of a difference.
Girona's most realistic target in the away match against Barcelona is to go home with 1 point. I'm sure it's difficult, but it's not a good idea to be too pessimistic about those chances. Of course it's risky to include Girona in the bet slip to win, unless it's just $1 for fun.