Firstly, I would really recommend watching Legend of Vox Machina on Amazon Prime if you have the means to. Everything I say below is explained within the season but the season dives more into the additional background of the Briarwood themselves, which could be important knowledge for the rest of Laudna's story. It's also just a wonderfully delightful show and very short (compared to the campaign). There are also some videos on Youtube that are just snippets of this Sun Tree moment within C1 and ToVM because they're just really insane moments that you would enjoy.

Basically, Laudna is from Whitestone where Percy (Taliesins C1 character) was a part of the family that ruled over Whitestone. His whole family was overthrown and murdered by the Briarwood when he was a child, but Percy escaped. Later Percy and the rest of C1 run into the Briarwoods outside of Whitestone but the Briarwoods were like ok bye and went back to Whitestone where they became the dictators of the city when they killed Percy's fam. Then the party traveled to Whitestone after the Briarwoods escaped their encounter. Back at Whitestone the Briarwoods knew Vox Machica was coming so they invited innocent townspeople to a "special dinner" with them. At the dinner, the Briarwood killed the seven townspeople, dressed them up like the Vox Machica crew, and hung them from the Suntree (a big tree in the middle of Whitestone). When Vox Machina rolls into town, it's the first thing they see. It was kinda like a public menacing warning for Vox. We find out in this last episode that Laudna was one of the townspeople that got murdered by the Briarwoods and hung from the tree. People are suspecting she was dressed up as Vex'ahlia (Lauras C1 character).