In my opinion the best way is to distract the younger one's attention at that point when the fight is on. And later show the elder one examples of people around her how they take care of the younger. You can also show something on the TV I am sure this will help.
All the best.

Fights mostly take place when kids are bored of playing with each other alone. It is always a good idea at that time to come in between and start a game in which both your daughter can be involved and they can play it happily along with you.

I am sure two girls would not fight as my 2 sons fight. Sometimes its so crazy that I am really scared. But along with the fight there is always one strong bond that they share. If a third person does something to one the other one is always there on his side. So, I guess this is the kind of bond siblings do share. Seeing my sons I remember my times spent with my siblings and I feel nostalgic.

So, will you I guess. I would suggest just take proper steps to handle the situation when there are fights and then let it be without worrying a lot. I am sure your daughters will grow into to lovely and smart girls and they will know how to share etc.

dunky, what comes to my mind I will like to share. If you can really do it this might work.
For about a week keep both your kids away from each other. Let them play on their own with each one's own toys. Make sure they do interact with each other for few minutes. Maybe for this their eating and afternoon nap time may be also made different for a while.
I am sure both will start missing each other and they would realise they need each other. After that mostly the number of fights will be less and when they fight remind them that they will have to stay alone if they do so.