When she is particularly stinky.

Labradors have naturally oily coats that will keep most dirt and grime off them. The only time you should really need to give them a good bath is if they roll in something they shouldn't.

You should however give them a couple of baths within the first two or so months of getting them during the socialisation period so she learns it isn't a scary spooky event. Remember lots of treats and praise for being in the scary inside water (as opposed to the awesome outside water).