@tanguatlay,
Yes, because the sentence makes sense without her name being used:
• Lee Hsien Yang described his elder sister to be "extremely unwell" in his latest Facebook post on March 7.
• Lee Hsien Yang described his elder sister, Lee Wei Ling, to be "extremely unwell" in his latest Facebook post on March 7.
But in a case like this, no commas are needed because the sentence is meaningless without the name:
• I read on Facebook that Lee Wei Ling is described as "extremely unwell" by her brother.