I can understand if it's a Chinese family drama lel.

Because in a Chinese family custom, the sisters marrying out is akin to collecting dowry to be saved for the brother use in his marriage.

The sister likely tah shiok because the downry her family received from her marrying to the mom's son will now be used back by her family (Daughter in Law side) to give out back to her husband's sister (mom side)

So that's like I kasi lu 100k angpow so you give me that BMW to ride, only for you to see that angpow given back over to my side in exchange for a perodua. (When this sense get into wimmin, naturally, they'll assume that the other one is a worst quality goods)