We would have to know way more information about this kid's skills and the reason her alignment is so poor on basic BHS. How old she is and how long she has been an optional would also be key in determining where to go from here.
There could be, and likely are, physical issues at play like scoliosis and poor flexibility. There's a possibility these things can be corrected, and that they will need to be if she'll have any success on this event.
Ain't that for sure. Is the problem that she's given up on the bhs, or does it seem more economical from a training strategy to detour around the bhs, or is her body just not built for them. If one of the first two questions are answered yes, I'd urge that the bhs goes through a complete retraining. The reality is if there are no outstanding physical or vestibular issues this skill is as simple as concentrating on centering your core, keeping your core tight, and letting the skill coast (no rushing the head and chest around, or the first foot on the step out) after pushing straight away from the beginning end of the beam.
But hey, kids can have the wackiest problems from years of weird, and maybe it's a lost cause. Here's a few ideas that I've resorted to, yeah...me too, for kids who had problematic back handsprings......
Roundoff back anything salto
Cross handstand or back extension roll-step down to layout-layout... but the step down has to be late, and if she thinks staying aligned on a bhs is tough, it'll feel like an eternity while falling from the handstand position to build up some linear energy.
Hey, have you had "the talk" about how the skills are only hard because you keep compensating for things you think you're not capable of doing right, or feels wrong (when it's not) so you come up with a genius alternative mechanical model that you *think* is making it easier.
You know, maybe her bhs will magically improve as soon as you read her the list of improbable possibles......
Side aerial- layout step out, or back salto tucked or piked but the kids I worked with tended to cut off the last bit of their set on the tucks and pikes whenever we messed around trying to find the easiest of the hard skills.
Skip this one if she has real issues in her back or shoulders........
Front headspring step out, or head kip, well any kip to kickover front. She can get into the spring/kip position from a forward roll or handstand forward roll..... or if the code allows use the headspring as a mount and connect into the kickover front.
Front aerial-front aerial
I would give her two days and two potential series to work with, and look all of them over on day three to decide which is better for her. Toss out the one that doesn't work, and move two the next two possible series and repeat the elimination process. Do not put two most likely ones together so each of those gets reviewed against some other series you may not expect her to take to....... but then again she may surprise the both of you and be well suited for what seemed the least likely.