Common livebearers from Asia are riddled with diseases and are inbred. This causes them to have a lot more health issues than local bred fish and fish that are from unrelated parents.
If this all started after she gave birth, then she might have been a weak fish to begin with and giving birth pushed her over the edge.
Another problem with livebearers is the females regularly become gravid (pregnant) when they are young (3-4 months old). This means they are not as well developed as they could be and there is more chance of them having complications compared to bigger older females that are 12 months old. Ideally, you don't want female livebearers to become gravid until they are at least 6 (preferably 12 months) old.
If this all started after she gave birth, then she might have been a weak fish to begin with and giving birth pushed her over the edge.
Another problem with livebearers is the females regularly become gravid (pregnant) when they are young (3-4 months old). This means they are not as well developed as they could be and there is more chance of them having complications compared to bigger older females that are 12 months old. Ideally, you don't want female livebearers to become gravid until they are at least 6 (preferably 12 months) old.