Is it okay for your best friend to vent to your boyfriend's friend that...

...she has only met twice? My best friend has a really loud mouth. She has no boundaries when it comes to telling people about her personal life. She has met my boyfriend's friends twice (and didnt even have a conversation longer than one minute with them at the time). She ran into my boyfriend's friend once at the mall and basically stopped him and had an hour long conversation (venting) about her life. When she told me about it, I told her she should not have done that, as my boyfriend's friends are his friends and my friends are my friends. I told her I barely knew my boyfriend's friends and that it was not okay for her to assume that because she had met them twice, that it would be okay for her to vent to them. She thinks Im overreacting.