Good to know it's nothing to get worried about. Her comb has also grown a lot recently - it used to be almost non-existent, but now it's the biggest of our three birds'. Is that related to her spur growth? Is it a hormonal thing?
I still find it hard saying three. To think we used to have seven...
All chickens, hens and roosters, have the gene to grow spurs. However in hens, this gene is generally turned off.
However in some older hens, this gene somehow comes back to life and they can grow spurs and even crow. All this usually happens in a flock with no rooster.
As long as she isn't turning aggressive, I wouldn't worry about them.