Some chickens will lay eggs their whole life and never go broody. Some will lay 3 eggs and try to set on everyone elses every few months.
Laying in and of itself does not mean the hen will want to set on them. It's a biological thing - some do some don't.
Silkies tend to go broody more than other breeds - but like gritsar said - they are individuals.
I have a brown leghorn who has been laying for three years and went broody for the first time this past summer. I have a barred rock and a few others the same age that have never been broody. I had a silkie (until the oppossum got her) that was always broody - I had another silkie that never went broody. Just for some examples for ya ...
If she's only just started laying eggs, she's still young as well. There is no way to force it to happen - and there is no way of telling if or when it will happen.