Alright but where do I find Sandra, cause it doesn't tell where she is and I think talking whit Bob might reveal her location which I think will be impossible to further the story.
You can talk to bob, you don't have to search the farm to do that.
When you do, just avoid talking about Sam which is irrelevant to the main quest. Just ask about Sandra.
Let me know if anything fails at this point, it would be critical!
But the main quest has been tested multiple times and working.