Hi there worried.. Welcome to HW
Well, firstly your mum is obviously a survivor..having had a bout of ?depression she has managed to keep herself together with out involving or worrying her family..wow she deserves a gold medal! As to the prob of approaching her about your find of meds and looking it up on the net - sheesh if it was me I would be pretty peeved in some respects..but in others relieved as everything would be out in the open.
By the way, those of us who suffer depression are brilliant actors lol..and can conceal our anxietys Most of the time!
What you choose to do is your biz..but it seems to me that she is coping really well just now...so you could just keep an eye on her and say nothing until/if you feel the need to share your concerns with her.
Wonderful that you care so much about your mum and have reached out here and asked for advice