Sally got a new car, and her bumper sticker read "My mum
s reward". On inquiry , understood that it was a gift. But now Im confused if 'Gift and Reward' can be used here ?
I interpret the bumper sticker to mean that Sally having a car is a reward for Sally's mum because her mum no longer has to chauffer Sally and her friends around to multiple activities throughout the work-week and the weekend. Reward is defined as something given or received in return or recompense for service, merit, hardship, etc. Since a reward is something given or received, most rewards can also be considered gifts or more precisely a particular subset of gifts which are essentially earned or merited. In this sense, Sally having her own car becomes a gift/reward for Sally's mum who had endured years of service, merit, hardship, etc.
The bumper-sticker is meant to be humorous, and also to call out recognition to Sally's mum. How Sally acquired the car is, in the end, irrelevant. Whether Sally worked to buy the car or the car was a gift or reward to Sally from Sally's Grandmother (and an indirect reward for Sally's mum according to the bumper sticker), or even if the car was a gift or reward to Sally from Sally's mum (and still an indirect reward back to Sally's mum - a sort of reward indirectly given to one's self), the meaning of the bumper sticker doesn't change.