It's really her Stage 5 appearances that cause so much trouble. Even on Easy, some of her attacks require the same tactics one would apply on higher difficulties. Perhaps I can give a few pointers for her boss fight:
First nonspell: It's just a matter of slipping through the lines of bullets when they reach you, and the lanes are spaced wide enough that you'll only have to do this once per wave. Just don't hit a stray blue pellet either.
First Spellcard: There are only a few zombie fairies on Easy, but this is one of those attacks I mentioned that must be approached the same way on all difficulties, namely by 'herding" the fairies. There are a couple ways to do this, but I prefer to start at the top of the screen, roughly above Orin, then quickly circle back down once Orin starts firing the blue bullets. The fairies will have followed you up top, and you can simply fire through them while near the bottom of the screen. The other way to herd the fairies is to lure them to one side, then circle below them (do not fire at them this time) until you have Orin in your sights. Fire at her for a bit, and when the fairies get close again, move to the other side and repeat the process. You'll essentially be making a sideways "figure-8" motion as you do this.
Second nonspell: Another attack with multiple approaches, but there's a way to trivialize this. Go up really close to Orin, as in right below her (I believe it's in line with the word "Graze" to the right). Because the bullets won't spawn within a certain radius of your hitbox, if you're close enough to Orin, you won't have to deal with any bullets coming from above. All you must do is tap down a bit when the spirits explode on either side.
Second Spellcard: The giant wheel's position depends on where you are when it appears. When the spirits start circling in, move up past them (don't ram one by mistake, let them be destroyed by your shots before moving) and stay within the lanes that come out of the explosion. Another wheel will spawn shortly after, so make sure you leave yourself enough room to repeat this process without getting walled - stay near the center of the screen, halfway between the Orin and the bottom, for the best results.
Third nonspell: The spirits Orin summons generate what can be described as a "randomly oriented static pattern". The directions the spirits are aligned rotate with each wave, but the bullet patterns they produce, as well as the safest locations to be, remain the same relative to the spirits. Generally speaking, try to stay directly between two of the spirits.
Third Spellcard: If I recall, on Easy, the spinning white wheels are actually aimed around you rather than at you. Thus you don't have to worry about dodging them. Merely stay under Orin and avoid the pink bullets as needed.
Fourth Spellcard: This card is a little unorthdox compared to some others, so don't feel bad about not being good at this one. The zombie fairies will move to your position when they first spawn - stay at the bottom of the screen and steadily move up toward Orin when they approach. The key is to deal as much damage to Orin as possible before this point. When you reach Orin, move to the upper-left corner (the general area, not the actual corner), and wait for the fairies to approach you again. Now move to the upper-right corner and wait a moment. The fairies will start firing their own bullets at this point, so dodge them and circle around under Orin, preferably near her position. Once again, the fairies will be up near Orin, and you can plow through some of them to damage Orin. Be sure to move down steadily if you choose this method, that way the fairies won't ever get too close for their shots to pose a threat. Don't be afraid to make another trip around Orin if you feel the fairies are getting too close, as even ReimuA can have a hard time keeping them down.
Hopefully this info will help. Again, keep at it - this is the kind of stuff that you'll improve at with lots of practice. Don't give up!
