Reddit mentions of Jssmst Locking Medicine Storage Box - Medication and Prescription Drugs Storage Box, 12 x 7.68 x 7.48 inches, Silver(MC17022)

To tack onto this it might be wise to keep all meds in a locking medicine cabinet that only you and your DH have the keys to. Not only will that prevent any accidents with your LO, /u/whtbrd, but it will also keep any guests- wanted or unwanted- from shopping around in your medicine cabinet [that way they can't steal any or tamper with any]. If anyone other than you or DH need something out of the cabinet either you or DH will go get it for them.

Poke around on amazon for a bit. It doesn't have to be something like this either, it could be something more like this, this, or even this or this as long as it locks well enough to keep unwanted people out. It doesn't need to be fancy. Don't even bring up the fact your worried that she might tamper with your meds to your DH, just tell him that your locking all the medications in the house- including yours- up so LO can't get to them and show him where the key is going to be kept.