Welcome!
About when to start, the BLW approach states that you could offer solid foods to your lo from day 1 and that she will only start to interact with it as a food when she is developmentally ready, so if Katie seems to be showing an interest in what you are eating at your mealtimes, and has the gross motor skills to sit up at the table with you in a highchair, there's no reason that you can't put a cooked carrot stick (or whatever you want to start with) on her tray and see what happens! If she ignores it, fine, if she pokes it, fine, if she picks it up and waves it about, fine, if she smooshes it to her mouth, fine, eventually as you model eating, and she associates her highchair with eating, and has access to foods, she'll work it out!
HTH?
Ax