reason

Guys the thing is that first shagun hated ruhi Bcz of ruhi sharam marriage broke and shagun thought once ruhi come ishraru cannot b seperated
Coming to point she now tell ruhi as meri beti Bcz currently ruhi is hating ishita so as per shagun wen ruhi will b released from Nidhi clutches she thinks ruhi will come to her( shagun) as according to her ruhi hates ishita
So
Today shagun called ruhi as meri beti Bcz ruhi hates ishita as per current track
Ruhi hatred for ishita= shagun calling ruhi as meri beti

This is the reason for calling ruhi as meri beti by shagun
Again wen ruhi ishita Unite that tym shagun will say woh (ruhi) meri kuch nai lagti