I agree with others, I don't think much of your trainer given the information you've provided. Drugging an injured horse so you can continue to ride it is, IMHO, one of the most despicable things that a "trainer" can do.
If the vet advised stall rest with a bit of turnout, then he certainly shouldn't be ridden at all until the injury/lameness is healed completely.
You definitely need to find a new trainer that has some compassion and common sense when it comes to horses. Whether that requires you to move barns or not, I don't know, but you need to get away from her one way or the other.