Okay. You haven't had a rooster for about 2 weeks. It's likely the eggs are fertile, especially with her being persistent about it. Chickens can and will hatch the eggs of their 'sisters', they just gather up what they consider 'the cream of the crop' and start sitting on the clutch. If you want more chick(s/ens) then by all means, allow her to sit. Not all breeds have an interest in brooding, I count my blessings when I get a hen that will. You said that this girl is young. Does she have the body fat needed to hatch this clutch without your assistance? Gently pinch around her breast bone to determine if she's plump enough to enable her to safely brood? If not, she will need supplemental feeding of high protein and high calorie food while brooding. Preferably you'll dish up these goodies to her in such a way that your big red girls can't get to it. Fat hens have reproductive disorders, often leading to death. Things to avoid giving her to snack on while brooding include vegetables, oats, rice, scratch, all of these will drive the percentage of protein down in her daily diet... the trick is to treat her with high protein and high calorie foods while she's brooding as she'll likely only 'grab a mouthful' here and there during this time; and again, you won't need to offer these supplements if you determine that she's plump enough to brood without dietary assistance.
If on the other hand, you do not want more chick(s/ens), then you'll need to put her into a wire cage without bedding to 'break her' of the desire to brood. I've read that it takes less than a week to 'break' them. Many articles on the forums here with detailed instruction on how to do that.