BlackKnight2016 is correct.
A LOA candidate only needs to be on the slate to get a nom.
Backing up a bit to your question. How does a recruited athlete in your district with a LOA affect your DD's chances.
It depends.
WP is obviously very interested in your DD with her acceptance to SLS and a LOE which enables her to go on an overnight visit.
The icing on the cake is that the Regional Commander has told her that she is #1 in her district.
So, let's assume that she is 3Q'd (which assumes medical is fine as well as the CFA).
Now she needs a nom.
Hopefully she has applied to all the noms that she is qualified for - which at a minimum is her 2 Senators, her Congressional Representative and the VP.
Her best chance is with the the Congressional Representative as there is less competition - numbers wise.
All MOCs (Senators and Reps) can submit one of 3 kinds of slates:
1) Competitive - MOC submits list to WP and they rank the candidates 1-10 based on WCS.
2) Principal with ranked alternates - MOC lists their choices for the nom 1-10 based on their own criteria. #1 will get the appointment, if 3Q'd even if a superstar is ranked lower.
3) Principal with unranked alternates - MOC puts their top choice as #1 and then the other 9 are listed unranked. WP will rank the other 9 based on WCS. The #1 will get the appointment if 3Q'd. If not 3Q'd, then down the list to the first 3Q'd candidate.
So - it really depends on what kind of slate your MOCs submit. If the LOA from her school is submitted on a Principal slate as #1, he/she will get the appointment, if 3Q'd - regardless of whether you DD had a higher WCS than the LOA candidate.
The best situation for your DD would be:
1) To be on a Competitive Slate. Her RC said that she was #1 in the district, so it can be assumed that she has the highest WCS in the district and therefore would be #1 on the slate. If 3Q'd, she would get the appointment. On the competitive slate, the LOA would be lower than your DD but can still get the appointment because they will have a nom even if not in the #1 spot.
OR
2) Be #1 on a Principal slate, ranked or unranked. The LOA could still be on these slates and get the appointment, since they will have a nom, even if not in the #1 spot.
Worst case scenario for your DD - the MOC submits a Principal slate and lists the 3Q'd LOA as the #1. Even then, it's not the end of the world as she will go on the NWL. Depending on how high her WCS is compared to the rest of those on the NWL will determine her chances of an appointment off the NWL.
If you don't know what kind of slate your MOCs submit, sometimes they say on their website. If not, you can call them and ask.
If she is 3Q'd prior to her MOC interviews, this tells the MOCs that WP has found her qualified for an appointment. This would be a sure appointment if they give her the slot.
So as you see - it depends.
I understand the stress. It's been 4 years since we were in your shoes and I can still feel the anxiety of the wait.
And you can really over think all this and cause yourself extra stress.
IMPO - she is in a good place. WP wants her.
Trust the process.