Daughters show that concern towards their parents even when they are living in another country with her family of her known.

As daughters they show care but as daughter in laws  they often do not. What could be the reason?

Dual standards. Double talk. Hypocricy.

Do such daughters deserve to be called apple of Dad's eyes?

Don't forget, the Saas is also a woman. She was also once the apple of her dad's eye.

Exactly,  I have often observed that in most cases women are troubling women and the men get the flak 

Somebody said aptly that woman is the worst enemy of woman.

Actually real gem of persons is parents they give up everything for the sake of love with their children.

Nowadays the advice is that parents should not give up everything to their children as they will then disown them and throw them on roads literally. Be careful.

True. Poor parents after giving away all the property with trust on the children, they will be subjected to untold woes.the moment the children get the property.