hhmmm..I'd probably troubleshoot whether or not she can't reach the adjuster, or she can reach it, but it simply son't "pull". Did she specifiy?
I know that on one of my old seats (comfortsport maybe?) There was a very specific time when it wouldn't "pull tight" because the splitter plate was right at this "turn" in the shell, right where the bottom versus the back of the shell meet, and my seats were very poofy in our van, such that when installed itghtly rearfacing, and spliter plate was actually underneath the carseat, and SMOOSHED uinto the poofy vehicle seats, such taht it didn't move easily..and then, if you loosened it, such taht eh splitter plate got pulled up, out form under the seat, and up the backside of the shell, and then tried to re-tighten it, you COULD NOT, because that would have meant pulling the splitter plate back UNDERNEATH the shell, which you could not do, because once you pulled it out, the seat poofed back up, and you couldn't get it back under there without uninstalling the seat.
so, I learned not to loosen it so much that the splitter plate got pulled out from under the seat, it had to stay underneath the seat. Does that make sense? i'm sorry..I coudl show you in like 20 seconds un person, but i'm really bad at describing stuff in words.
I've never installed a MR IRL, so i don't know how the path for the aplitter works or if that is even a remote possibility, but I did have a seat you "couldn't tighten" before.