Lady Maria is, in my opinion, the best boss in all of the Soulsborne boss library. That said, she's not the easiest boss. Not the hardest, but not the easiest.
You can fight her without parries if you want an added challenge, but for new players the parry is the way to go, I think. She has obvious windows in her first phase, but as the phases go on she gets more and more difficult to parry. That's okay because if you're doing decent enough damage you can pretty much skip her third phase.
So I like to open with a parry. Like Father Gascoigne, she will stagger if you do a transformation attack on her (R1/L1/L1). If you're building beast meter you will start to output more damage, too. You can get some hits on her when she is going into her second/third phases, but she does an AOE so get in 2 or so hits and then dodge away from her. I mess up and dodge too far back. You want to stay mid-range for this fight. If she closes the gap you can dodge at a diagonal towards her which will miss lunging attacks. If you want to fight with Charged R2's just know that if you are locking on you might miss so...cancel the lock on if you are trying for R2's to the back.
A great fight and you can really do this without taking any hits or using any vials if you understand that her action is fast but comes in bursts. Navigating those quick bursts can be simple if you get the parry time down, or use transformation staggers to your advantage. With each phase she gains more and more range, blood attacks in phase 2, and then blood AND fire attacks in phase 3. You want to end this as fast as possible if you want to avoid a hard fight OR...take her on for all three phases. It's the most fun and intense fight in Bloodborne and deserves to be played over and over in multiple ways.
![](https://i.ytimg.com/vi/hf_CDEhJfX0/mqdefault.jpg)