Ewwie, ok thanks.. Then it's a no on the coconut shell.. Glad I asked, coconut ice cream came in it and as soon as I seen it I thought how Rosie would like to play in it and how she would like to drop her little toys in it to hear them make that little click noise when they hit the bottom.
Yes, they are used for toys with bigger birds that cannot sit inside them and see that they resemble a nest. I wouldn't even use one for my ringneck, and she is much bigger than a tiel. Since Rosie is already nesty, there is no need to encourage that behavior.
The other thing that would make me say no is the fact that ice cream used to be in it. It would be very hard to make sure all the residue from it was gone since coconut shell is porous.