She and Sharon are amazing at 5 stars.
I already have them at 4 stars and they've been doing very solid jobs.
5 Star Anna has high attack, high speed, and high resistance. She gets a weapon that allows her to warp to any ally at 40% HP. She has Vantage and she gets an ougi that multiplies her damage by 2.5x
She's very good as a green character and provides things that other greens don't provide.
Sharon is bulky enough to take hits, fast enough to not get doubled and can support her party with attack and defense buffs.
So you really think it's worth spending feathers on them?