My party level was 31-32 when I fought her, and this was a challenging fight. She's very fast and will counterattack everything you do. The only way around this is to stay on the back row where her counterattack can't reach and peck away at her HP with long distance attacks. She can still reach you on the back row with her regular attacks, but this will only hit one character at a time. Have plenty of healing items for when she uses Sakura's Dream (reduces HP to 1). Just stay healed and be patient. Don't get close to her until you're sure you can finish her off.