Thank you. Samuel Candace

In English, the word "yell" is often associated with angry feelings. If the woman was calling her son in an angry voice, I would say, "she yelled at her son to get her medicine". You could also use the word, shout, which suggests louder volume and authority. For example, "she shouted at her son to get her medicine". Another suggestion is, "she cried out to her son". This suggests more desperation and fear in her voice. For example, "she cried out to her son to get her medicine". Hope this helps

Hey XiaoDeng, Usually "yell out for" is a request to someone and "yell at / yell out at" is an instruction or command.

In this context you could use “yell out to her son” or “for her son.” The word ‘for’ gives the impression that the son is far away, like in another room. ‘At’ would make sense but it makes more sense to use ‘at’ if the son was getting yelled at for something, for instance, ‘she yelled at her son for breaking the lamp’