What did she lose, personal things, anything of value?
I know losing anything is awful but trying to establish if there's any claim there if anything expensive was gotten rid that she can prove value (eg receipts) for a small claims action.
Has she definitely put it in the rubbish or could she be saying that to wind your daughter up?
If that may be the case or in any event, you could ring your local police station and ask for their advice but criminal is not my thing so don't know what their reaction may be.
She won't get her stuff back if it's been taken so however hard it may be it's gone and there may be little she can do.
May be something she just has to put down to experience and move on from.