Wow. Kudos to you for having a White Leghorn go broody. They almost NEVER go broody due to being selected for egg production generation after generation, which of course deselects for broodiness hormones.
So I'll treat her a bit more delicately as it will be amazingly awesome that she goes the full 3 weeks. (It's been done by others on this forum with WLs, so I know it's possible).
Ideally, she should have her own isolated corner with her own food and water, especially for a first time brood with a first time flock with a broody. (Eventually you get a chill flock that accommodates broodies well, but that can take time and is a bit riskier.)
I would avoid attempting to move her to a better place due to her WL genetics. If she is in a terrible place, now would be the time to move her, but let's try to work around her instead. (Which sounds like you've already done). Moving many hens will break the brood, and since we (I) don't trust her WL genetics are that strong, it's probably best to simply partition her off rather than attempt moving her. (With a Silkie, you can pretty much plunk them anywhere, give them something in the shape of an egg, and they'll brood.)
If you haven't done so already, mark the eggs she is sitting on. ALL eggs should be set at the SAME time to avoid a staggered hatch. I like to mark with the date set (as I tend to forget). Then mark on your calendar 21 days out as hatch day.
For a standard WL, I would recommend no more than 10. For a first time mommy, I might not go over 8. (75% typically hatch, so that means 6 babes to care for).
If other hens are still laying in that nest (it would be nice if they weren't), then you'll have to remove new eggs daily (easy as you've marked the original). Do that at night with a strong flashlight.
You can candle at day 5 to check for developing eggs. To educate your eyes, pick up a non-set egg and shine through to see what clear looks like. Then check your set eggs. At this point you should have a bean shape dark spot with road map veins going out. If you've got darker brown eggs or blue eggs, it will be harder to see. You may just see a darker cloud in the middle. Remove any all clear eggs.
Let her sit and sit. You can recheck again at day 14. At that point you should see a big dark blob at one end and a clear air cell at the other. If you have any clear eggs at this point, remove them. Likely you will have some ambiguous eggs. Leave them.
Let her sit and sit. Resist the temptation to constantly check and peek starting with day 18. If at all possible, skirt her nest with some sort of fencing to give her complete privacy. This is considered lock down, and she shouldn't have to accommodate other hens laying in the nest. If a new egg sneaks in, leave and toss after hatching is done.
Day 20 start listening at the nest without checking under the hen. By day 21 (often on 20) you should hear some cheeping. Really, really resist checking under the hen as many chicks are halfway hatched and you can cause a shrink wrap or unnerve the hen so she abandons the nest. Day 22, check under the hen. Remove any broken egg shells. Candle remaining eggs to see if they are developed. At 23 hen should be up and scratching with babes, taking them to food and water (which should be nearby but not so it can tip into the nest).
Good luck with your WL, and congratulations again.
LofMc
