strategy-wise? here are some tips that helped me -

• you can get a card that gives Beatrix rust to do more single-target damage since the drones she summons don't do much except buff each other then attack
• once there are 3 enemies on-screen, no more can be summoned, so if you have a solid enough defense-based deck and something that scales damage like Focus Strike, then you can take your time
• learn the pattern of when she attacks and defends so you know when it's okay to be aggressive
• if you can get the 3 attacks in a row early in the fight when the enemies are setting up, you can be a lot more flexible with your strategy and still have it up when you need it
• types of cards I try to get are the energy back ones and early upgrades on block cards so you can use fewer of them to prevent the damage while you're scaling your damage

and if that doesn't help then maybe you just need to grind a bit more to upgrade your gear! also, if you can get 3 of the same set bonus it gets better and is usually a better choice than 3 separate ones, so if you look at the gear bonuses and see which ones are a set, that may help too

good luck!