自己 - by oneself?
我刚学了《反身代词》那个课。我知道“自己”的直接翻译是"myself, yourself"等等，所以 "她自己说过那个。" 应该翻译成 "She said that herself." 在这里意思是要确定就是那个人做的动作，不是别人。这个我没有问题。
不过，我原来不知道“自己”也能翻译成"by oneself"，因为"by myself"的意思是“我一个人”。我看见的一个课里面的句子是“你们自己去的吗？“，他们给的翻译是"Did you go by yourselves?" 在这个情况下，"by yourselves"的意思是只有那些人去了，没有别人陪他们去。在这里使用“自己”也是这个意思吗？我只要确定，因为以前没有看过。
Yes, 自己 can mean both "oneself" and "by oneself". But there seems to be something wrong for the sentence "She said that herself." appear in reflexive pronoun. Just a few clarifications.
Reflexive Pronouns: oneself. Used to indicate the receiver of the verb is exactly the agent. ex.: He washed himself. In Chinese, 自己 for this meaning appears after the verb (and sometimes in informal chatting, an additional 自己 may appear before the verb, as 自己verb自己).
Intensive Pronouns: oneself (the same form as the reflexive). Used to emphasize the (pro)noun(s) mentioned. ex.: She said that herself. It can always be paraphrased into It is she who said that. In Chinese, 自己 for this meaning appears after the (pro)noun(s) it emphasizes.
By oneself: A adverbial phrase indicating the action is done by the agent(s) exclusively. ex.: Did you go by yourself? In Chinese, 自己 for this meaning appears before the verb or after the subject. The Chinese syntax in this case is more flexible, so it may be confusing to distinguish this case and the second one above.
"by myself" 的意思 是”我自己一个人“， 并没有别人陪我。 比如说”I am eating dinner by myself", 就是说“我自己一个人在吃 晚 餐” ， 没有人作伴。
"by oneself" 就有点不一样， 虽然它也带有“自 己一个人”的意 思。 这里所指 的并不是发言人”自己“本身， 而是 "一般人自己“ 。 以下有一些例子，可作参考。
by oneself: http://idioms.thefreedictionary.com/by+oneself
with no one else present; alone (of two or more people) -- Must one sit by oneself or may one join another group? -- One just hates eating by oneself, doesn't one?
with the help of no one else -- One is expected to do it by oneself. Can one do this by oneself?
我用的是"by oneself"因为“self”那些词都有不同的形式，比如"myself, yourself, himself, herself"等等。在这个情况下，使用"oneself"指的是“self”的这些所有的形式。
Oh. I am sorry I misunderstood you. Yes,"自己" can also mean "by oneself", i.e."没有别人陪". Whether it means "oneself" or "by oneself" depends on the context.