First time post so be gentle with me

My great grandparents were born in Ireland but my grandmother was born in Scotland, as was my mum.
If my mum was to now register on the FBR and gain citizenship by descent, would I subsequently also be able to apply for registration on the FBR as her descendant? I don't know when the whole FBR became a requirement and whether my mum would have needed to be on the FBR or whatever was in place at the time she was born (1946).
I've looked at the FBR website for guidance but it's still not actually clear to me!
Thoughts/comments gratefully received. My husband has successfully gone through the process and now has his Irish passport. I want one too!

Thanks
Shimit