Hi there! In order of your questions....
1. Those are spur buds! Contrary to popular belief, hens can have spurs. I have two Buff Orpingtons who both have spur buds much larger than those on your girl.
2. I doubt your hen's spurs will ever injure any other chickens. From my experience, the spurs a hen grows rarely compare in size to those of a rooster. In fact, mine have sort of stayed at the bud stage, rather than grow out to full curved spurs. Even if they do grow longer, most hens don't mount other chickens (unless there is a hormonal issue at play, or there is no rooster in the flock), so it is unlikely she will injure another bird with them. Roosters can occasionally damage hens with their spurs, but that is usually done during mating.
3. She can keep her leg rings, but if it worries you, you could remove them. I do a check of all my bird's leg rings every month or so to make sure they are not getting too tight, but other than that the spurs should not affect how she wears the leg rings. They will just sit over the top of the spur as they are now.
4. No, the spur buds won't harm your girl. She will be just fine. It's completely natural for her to have them.
5. I am not aware of any link between spur buds and aggression. My BO's are just lovely, and have never been aggressive. It's easy to link spurs with aggression, because usually it's the roosters that have spurs - and roosters are more inclined to be aggressive! That being said, there are many, many roosters who are just big cuddle-puffs too! My roo is a big sook! Don't worry, your girl is no less a girl because she has spurs.
So, to summarise....
Everything is completely normal and there is nothing to worry about. She will go about her chicken-y business with or without spurs, and it is highly unlikely that those little buds will ever be a problem - to her, or the rest of your flock.
My best wishes to you!
Krista
ETA: My girls started growing their spur buds at 6 months.
