If you don't need the money to cover the additional costs associated with her living there then don't do it. I personally don't understand why parents charge their children rent "just because". It doesn't make sense to me.
Yes, living at home for free if on a good wage is a privilege, but surely this will then just allow the child to save more and put towards a deposit and get out of the house quicker.
I don't get why parents of adult children spout on about "but it's way cheaper than if they were renting/living in a house share" - yes we know that too, but again it doesn't mean you should automatically be charging rent just for the sake of it.
Having said this, it very much depends on the child. My parents don't charge me rent, however I am basically a housemate in terms of I buy all my own groceries, toiletries, clothes etc. Pay my own car related costs & do everything myself so do my own laundry, cook all of my own meals. I don't rely on my parents for anything but them not charging me rent means that I have been about to save up a large chunk of money towards a house deposit.
Obviously if the child is costing you money/you can't afford to have them there for free/ they are reckless and fritter away their money then you may want to charge them a small sum.
Also, just because I'm living rent free doesn't mean I don't know the value of money as some other posters would suggest. I lived away at uni for 4 years and had to work to add to my student loan to be able to cover my rent and living expenses. Also I have to pay all my other bills and expenses so I don't agree with the fact that if you don't pay rent somehow you're living in the clouds and have no clue of what things cost.
But if you're doing it just for the sake of it then I wouldn't.