I would give best friend a chance to explain all your concerns in face or in phone.
Even she did say something bad about you in front of "other people", is that really a unforgivable mistake?? Who do you have higher regard in heart, her or them?? If it is her, I would think that you will feel more sad about losing her friendship than other people. Who cares what they think about you? I only care about my family and friends.
If you think she has such an influnce on other people, "有時候要在國內找找關係熟人之類的", why not ask her for help. If she is indeed the trouble maker, then she might want to mend it for you. You should bring her to the side of "helper" instead of the side of "distractor".
Don't easily break a relationship so treasurous to you in the past. It's like glass - once it is broken, it will never be mended again.
