I wouldn't search her room. When my mum took my knife (without knowing I SI'd) I simply bought another one.

Instead, ask her to turn in the implements she uses. Put them in an envelope - or ask her to do it - and tell her you'll take care of them. You might even want to write on the envelope what's in it - a knife belonging to ** (your daughter's name). Then hide them or throw them away.

It'll make them out of reach, but not away. Away implies it needs to be replaced. Out of reach means it might have to be found some day.

It worked for me for a while. A far longer time than my knife just being taken from me.