Originally Posted by
Kratosirving
She's okay. Honestly as a Moon Cancer she really suffers from only having super-effective damage against Avengers/Zerkers and neutral to almost everything else besides Rulers. Her card lock skill makes her amazing to use if you build a specific team; can be around her as a crit DPS with some support, or to help setup Star gening or Arts looping with other Servants with her as a support. She gets decent passives to help her damage, and her NP will drain one tick of an enemy's NP gauge with a small chance to drain two ticks if you can get a high Overcharge on it.
tl;dr though is if you've got a dedicated AoE Servant for all 7 regular classes you can use and/or have supportive Servants that can more reliably help with Star Gen or charging NP gauges, you'll likely only ever bring her out to help with the odd Avenger enemy, and even then you might be likely to bring her Welfare 4* version because she has a ST NP while Summer BB has an AoE one. :|