Not sure what to do!

So...my eldest girl who is 4 sometimes goes around to a friends house to play after school and i pick her up after a while. The other day we saw the friends Mum (who seems really lovely and i have known her almost a year), but my DD said she did not want to go around, which is odd as she always jumps at the chance. This morning while i was getting her ready for school she started telling me how her friends mum got cross as her friend had been very rude to her and apparently she waved a 'big knife' (she was cooking at the time) at her daughter saying she would cut her tongue! I was in disbelief and asked if my DD was making up stories (she doesn't really do this and would have no idea where she would get the idea) but she was adamant..i feel quite sick in the stomach.i don't want my little girl going anymore.do i ask the mum about this? do i avoid her altogether?