I tried what you just said and it works fine for me, she just gets the steroids effect and you can keep training her. You're the first one to have that issue, you sure you didn't do anything else? From what I can see giving her steroids early doesn't affect much. Also I'll change up Mia's training next update anyway, we'll train her at the gym in town instead of at home.
umm.. i got a question. is that how it's supposed to be(0.1.6)? or it's fixed in 0.1.7? bought massage gun and weights and used both on myself on first stage of Mia's growth.
edit: I saw you replying to zabra1212 recently. I have same problem. got Mia to level 3, got dialogue and she still remaned being level 2. gave her no steroids though.