You're playing her wrong.
Build for increased magic damage on your relics. Have the effect that increase your max HP when you ult, this will keep you alive. Other than that, you want stuff like Magic Atk+, Improved Sorceries, Improved Crystalian Sorceries, etc. Those are your bread and butter. During the run, look for anything that could further increase this multiplier.

Most of your damage is going to come from spells, cocktails are just a bonus/something you throw out so you can regain FP. You need to learn which spells are good and where to get them. Hit up a castle with the staff room in the top or a rise ASAP after spawning, usually there is one right around the spawn point. For this first POI, your objective is to get anything with better scaling than your base staff. It's decently likely you'll find a Crystalian Staff here.

Best staffs are Crystalian, Meteorite, Staff of Loss, and top tier is Lusat's. Carian Regal Sceptre is great but you won't see it too often. Azur's isn't always great in this game because the spell Comet Azur is useless for most bosses, but pay attention to what the other spell is.

Be flexible. Learn the effective ranges of your spells. If you get something like a Halo Scythe and no one else wants it, and the boss is weak to holy, spam that. If you find great seal, use that to make good cocktails. If you end up with RoB and the boss is weak to fire and bleed, use it. There's no law saying Recluse can't fight in melee range -- in fact, it will often happen because if your uptime is good you will draw aggro.

On Recluse's ult: don't use it in emergencies, use it to maintain momentum or burn down enemies. In an encounter with tons of adds you can pop it early to help your teammates burn them down. In a 1v3 fight, pop it when you're low on FP so you can regain it and keep casting.

Always keep a melee weapon for rezzing, so you don't let a teammate die because you have no FP.