Dani Ramos: How do we win?
Grace: We win... by keeping you alive.
Dani: What did you tell them?
T-800: I told them you coming here makes this place unsafe for them. Also, the day I warned them might come, has come. My past has caught up with me. And...I won't be back.
Sarah Connor: I'll be back.
Grace: Who are you?
Sarah Connor: My name is Sarah Connor. I've never seen one like you before. Almost human.
Grace: I am human.
Grace: Why do you care what happens to her?
Sarah Connor: Because I was her.
Dani Ramos: Two days ago, I had this nice, simple life. And now it's a nightmare.
Sarah Connor: My name is Sarah Connor. August 29th, 1997 was supposed to be Judgment Day. But I changed the future. Saved 3,000,000,000 lives. Enough of a résumé for you?
Grace: No. You may have changed the future, but you didn't change our fate.
Suggested correction: Sarah is very skilled at fighting Terminators. She receives the coordinates but knows that many other real-world factors may impede her progress to those coordinates, so she makes efforts to prepare for that. Also, the coordinates that she received for the Rev-9 may very well have told her to fight it on the bridge because the T800 who sent those coordinates knew that Sarah would also then be able to rescue Dani and Grace, and eventually meet up with him as a result.
I'd say the real reason Sarah is on the highway to fight Rev-9 is that she followed it. She misses the moment it arrived (from the future), she follows it to the car factory, but she misses it again, then she finally catches it up on the highway.
It is explicitly stated by the T800 Carl that he was sending Sarah the coordinates of where the terminators would appear, because the arrival would create a space-time wrinkle he is able to measure ahead of time. There is no indication he can predict the future events and send Sarah coordinates of places to be other than that.
Epigenis
Suggested correction: Sarah's truck can be seen in the background when Grace arrives. Grace doesn't look like any Skynet Terminator, and the time bubble she arrives in is different to the ones in T1 and T2. We can infer that Sarah followed Grace from her arrival to the bridge in an attempt to understand what was going on with the new time travellers before intervening.