Well, it depends on your DD's cognitive profile, personality traits and other general essential skills (writing, executive functional, social, emotional) as well as each individual teacher and each educational institution (including interacting peer groups).
For example, I know a public middle school(not our school) that has many many students who qualify for AIME (by top scores on AMC10/AMC12) as well as some who qualify for USAMO/USAJMO (by top scores on AIME).
Whether your DD finds challenge within her particular middle school will depend on her personality as well. Middle schools around here tend to be product oriented (writing as well as multi-media)so it is up to the student how deeply/broadly they want to research and what level of work they want to produce.
If you want to find out what your DD is capable of, then consider signing her up for the SAT, particularly to see where she is and if she is anywhere near the ceiling on the verbal. For math, the ceiling is not particularly high as compare to many competition math problems. You can start her on the AMC8 (easiest of the AMCs) to see how well she solves non-routine math problems..
Yes, executive function is the name of the game here. DD is ADHD inattentive type so we will be all over that issue. Luckily I have seen her improve 1000% concerning homework. She just gets right to it, no fuss, no bother! Amazing! Even the lunchbox has been coming home!!

Social/emotional? She seems to be doing better, and appears to have more friends now. We will be watching closely next year. She was one of the younger 4th graders so now is a very young 5th grader. Put her in the middle of a bunch of kids going through puberty? Big concern of mine. Question -How does one deal with a child who is younger than average who sees all the "big" kids get cell phones, electronics etc . Do you go by age or grade level? Children want to fit in.
Well I have to claim ignorance of AIME so I am off to research that! And when you mention the SAT that feels so foreign to me as my DH and I took it late high school as is typical. DD was set to take the Explore test, but we had a death in the family that same weekend.
Another point - I have heard that middle school here is also project oriented - THAT - will be fun for DD. She writes all the live long day and loves Power Point, Haiku Deck...