It appears to go back to the ancient Greeks and Romans who worshipped their 'Maternal goddess' as part of their spring festivities.
The modern British "Mother's day" has no direct connection with the American one. It certainly goes back to the 1600's in the England. Originally, it would have been the day when people made a pilgrimage to their "Mother" church, and later when many young women worked as domestic servants, it was a day when they were allowed to go home and give gifts to their mothers.
I'm afraid that I'm a cynic when it come to these things. Like other festivals, it has become commercialised and yet another way of relieving people of their money. It's just another day in the Lightning household.