The sentence "She has gone to America and she'll be back next week" is good because "has gone" suggests that she is away in America now, and because of that, you cannot say "She has gone to America but she's back home now".
And the sentence "She went to America but now she is back at home." sounds good, right? ; my question is whether I can say "She went to America, and she'll be back next week."
To sum, if you use the present perfect there is only one way of continuing, but if you use the simple past, in principle, there are two possible continuations, so in the above situation, if "... she will be back next week," simple past and present perfect can be used interchangeably, although present perfect may be a preferred choice. Am I right in thinking this way?