Beidou has a parry mechanic that may be difficult for many people to utilize, but fortunately, fun as it is, it's not Beidou's main feature. As long as players can maintain enough Energy for her Elemental Burst, Beidou will surely perform.
Beidou is a great sub-DPS to be paired with many characters. She works great in a Firework team with Hydro DPS, or Quicken team with Dendro.
The main role for Beidou is sub-DPS, but she also fulfills the support shoe, and can even perform as a main DPS if required.
When it comes to World Boss, Beidou is not the best option. Players won't be able to fully utilize her Burst, and since most of her team revolves around Elemental reactions, some boss' Elements will ruin it for her party.
With the correct teammates, Beidou can be a valuable character to have within the Spiral Abyss.