FWIW, would recommend that your child does the AoPS preAlg before anything else.
We also live in a rural area (within low shot as well as bow shot of real live cattle) so we too have felt the pain of having a child that would be an outlier in city populations let alone where we live.
We managed to get our child's 4th grade teacher to allow her to do the AoPS preAlg chapter work (we would print it out so as not to make her too conspicuous) during class time and then do the class one evening a week. After doing this class she ceilinged on the Maths section of the Explore.
In 5th the wheels came off a bit as the Maths teacher was very anti-gifted so our child had to do the AoPS Alg I after school which sucked a bit but she stayed interested and challenged (just not in school).
Middle school starts in 6th here in our SD and after a placement test that the teacher did her best to sabotage DD still was placed into the CC 'advanced' Alg I class (8th grade). We went along to try to get her in a class with more 'peer like' kids. Now almost at the end of the year DD reports that AoPS preAlg was harder so the link up thread about Alg I being diluted may have some merit.
Next year DD will be bused to the HS honours Geometry program which will be on trial as far as we are concerned. Maths is first period so if DD is not comfortable in the HS (she is 11) then we will just have her do the AoPS Geometry from home and then take her to the MS for second period on. If the HS works out then DD will circle back through the AoPS curriculum once done with PS Maths.
We are in no hurry for her to go to college - she has been whole grade accelerated already and while she complains about the slow pace of everything we are not willing to put her through any more skips. This seems to be the best plan given what we know so far but we have already learned to write plans using pencil not ink LOL
One thing that I have to say that I am deeply grateful for is the MS principal and her current Maths teacher have been massively supportive of our DD. I read posts everyday here about the willful ignorance and pigheadedness of some SDs - my DD is online friends with a fellow DYS girl whose mother is a frequent poster here, her friend has an even higher LOG than her but a much stupider SD administration so she is still stuck in regular 5th grade Maths
A lot just comes down to luck...
