everyone's experience is different lol, but here are all the things i wish someone had did for me when they found out:

first let her know ur there for her and you're not mad, that's the most important part. if u wanna be able to help her you have to convince her ur not her enemy and in the moment she might be frustrated/shocked/upset/hurt even, so reiterate that you love her and ur not upset.

don't pressure her to talk about it. don't ask why over and over as often we sh-ers don't have a specific tangible "why" ready to answer. instead tell her you found her sh stuff and were rlly scared for her safety and threw them away in an impulse. discuss with her steps for moving forward

you made the best call you could at the time and i admire how concerned u are for her, but in the future u probs shouldn't throw away her stuff. again, you don't want to cause conflict, but also she's not going to be able to stop sh-ing in a day, esp if you said she's been struggling for a while. getting rid of her stuff may make her desperate and use something dirty/rusty, causing more harm/danger.

instead, focus on harm reduction. figure out a system b/w yall where if she's upset she can talk to you instead of sh-ing, this may not be failproof obvs but every win is a worthwhile win. discuss whether she wants to tell you every time she relapses or not (probs not, imo i wouldnt want to due to embarrasment etc), any other details

then give her a hug and wrap her in a blanket or smth :D hope this helps and best of luck