You can put it under her pillow, for the tooth fairy!
If you decide to keep the baby tooth, then you can do the following:
1. Wash it under running tap, to remove any remaining blood clots or stains.
2. Is the baby tooth decayed or sound? In either case, you can remove the bacteria by disinfecting it in any houshold bleach for 24 hours. After soaking, just leave it to dry.
3. After that, you will notice the tooth has turned whiter, and it is alright.
The above steps are applicable to adult tooth too, if you decide to keep any of your adult tooth, eg wisdom tooth after extraction or surgery, teeth taken out for orthodontic reasons, etc
It is now safe for your girl to touch and play with. Be careful with younger kids or infants, do not allow them to insert the little tooth in the mouth.
You can keep the tooth in any little box. Have fun in collecting them all !