I have 2 kids, like you, and my daughter is older and my son is the younger one. My kids are 4 years apart.
NOW, what I did, from the moment my son was born is: I, REGULARLY... explained to my eldest, (in a way she can understand), about HOW her little brother is developing... how because he is younger he does not and cannot know everything she does and does not understand things as she does etc. I explain it in a way that is nurturing and not taking sides. THIS HAS HELPED her immensely... when she is irked with her little brother.
It made a huge difference... in her empathy/understanding/ and patience with her little brother.
BUT at no time, do I favor one or the other. And at no time, do I use her little brother's being the youngest as an excuse for him doing certain things to her. If it is wrong, it is wrong, etc.
I ALSO tell my eldest, that... SHE is a child herself, and I in no way expect her to be perfect NOR to be the "example" for her younger sibling. Because, I do not want her to feel pressured nor burdened... that SHE IS the one to be good all the time. BUT that, she CAN and should tell me anything that bothers her... so that I can understand her as the oldest... and help her.
Per "blaming"... my kids don't really have that problem in a chronic manner. BUT when it occurs, I tell them that it takes 2. It takes 2 to make a problem and it takes 2 to help stop it and work it out. I ALSO tell my kids... that they need to respect each other.... they are siblings, not competitors. They will have each other ALL their lives and they need to be there for each other. My kids are close. Like 2 peas in a pod. I teach them to be a "team." I teach them to know each others cues. ie: If my son is telling my daughter to stop bothering him... she needs to heed to that. Because, her little brother is trying his best... to say it nicely. AND that, she knows DARN well... that the more she irks him the more he will get MAD. And then a fight occurs. But it is because... she did not heed to his cues, in the first place. Likewise, for my son- IF his sister is doing homework and he bothers her... and she gets irked, he needs to stop. Why keep irking her and then making her MAD, too? And that... they KNOW darn well, when they are irking the other on purpose or not. So if the other sibling gets mad... well they knew that would happen. SO, learn the cues of the other, and the limits, of the others.
Blaming.. is not tolerated. I tell them that.
And, when it is ridiculous, I tell them... and they know it.
HOW on earth, can they blame the other sibling when that sibling was in ANOTHER room completely? Duh. So that is ridiculous and not, reasonable. At all. They KNOW that.
Again, "blaming" is not tolerated... BUT they CAN tell me when/if something is bothering them, that the other sibling did.
And I also teach them the difference between: if they did something ON PURPOSE to the other, or if it was just a mistake or done unknowingly.
They know that.
Your daughter is using her younger sibling as the fall guy.
And she may resent him, because he is younger and therefore she may think he gets more leeway.
You have to figure out WHY she is constantly blaming him.
And/or if they are just irking each other on purpose.
Because then, kids get frustrated and mad. And that means they are BOTH wrong.