I find this hard to believe, both cases would be 25kg each, she must have noticed the weight.
When she got ready for the flight the next morning did she wear all the same clothes she had on the night before or did she wear a new outfit, if a new outfit, she must have put her dirty clothes in one of the bags containing 23kg of weed and somehow not noticed all her original luggage had been removed. Could possibly have put everything in a carry on bag i suppose.
A small lady would really struggle to lift 25kg in each hand if you ask me, and surely they were not 25kg each when she packed them for a "short trip" to Sri Lanka.
Maybe it is all lost in translation and the bags were tampered with after being checked in at the airport.