What is the purpose of
已 in the following sentence？
The English translation given is:
It looks as if she's gone away for a few days.
Or is this an incorrect-character, supposed to be something else?
Here 已 has the same meaning as 已经 and means already. When speaking one would normally use 已经, but in written documents 已 can be found.
I would translate 好像她已出去好几天了 as "It seems she's already been gone for some days".
Indeed "It looks as if she's gone away for a few days" is an incorrect translation.
I would translate this as "It seems she's already been gone for quite a few days".
If the 已 were excluded, I would translate it as "It seems she's been gone for quite a few days."
So the 已 emphasizes the passage of time, just like "already" in English.
已=已经. It just represents the past perfect tense. I think [been] is necessary here. The sentence implies that the subject never came back during the few days, in this case past perfect tense is appropriate.