help?

hey recently one of my friends had a friendship problem and idk how to help her.
She is best of friends with another girl called x. she is a playful person and occasionally hits x playfully maybe sometimes a bit over the limit but tts just her. however recently x got angry and told her mum bout it. her mum called my friend and scolded her(e.g do u want my daughter to end up in the hospital etc..).

my friend was hurt cuz she was just playing n didnt expect x to take it so seriously. since then they are not as close as before. My friend is deeply hurt and seems very sad and out of herself lately. she has apologized as well. but x doesnt seem to care. she goes out with y who also told my friend tt she is the bad guy. she tells me about these stuff and is very upset. How can i help her and improve the situation?