Giving a quick look over her statistics and backstory in the first volume of Reign of Winter, she seems extremely well suited to being a ranger. Of course, barbarian isn't an awful fit, though she seems very 'patient' for a barbarian. She's undergone a lot of awfulness in her life with a seemingly 'grin and bear it' sort of attitude. Of course if your PCs inform them of her child's fate, it could be the 'final straw', sort of situation.
As far as rules go, she seems to be built as a switch-hitting sort of character, thanks to Two-Weapon Fighting and Point-Blank Shot being feat picks.
If you go barbarian, I would suggest using the Unchained rules, as they do a much better job dual-wielding. Personally, I'd keep her as a Ranger, perhaps with an archetype (perhaps guide, warden, or woodland skirmisher? Two Rangers in a party isn't necessarily a bad choice - as your characters level, have her specialize differently than your party's Ranger, such as making her an archer if they go melee.
Another interesting option that wouldn't be an awful choice for your group and could prove thematic would be a Skald. It seems an interesting fit, and could be a very good choice as a fifth party member's slot. In addition, if you choose Skald for her, it gives her a good space as a supporter so the PCs don't feel overshadowed by an allied character.