I have not read the books. In the HBO presentation Daenerys incarcerates two of her dragons in some sort of dungeon. After evidently neglecting them, she is horrified at their size and anger when she visits them in Season 5 episode 1.
Her abandonment of the dragons until that point seemed out of character and irrational in regard to her aspirations. Why didn't she spend time with them and play with them?
The TV special seems to give no thought to their ever growing size and fierceness in terms of controlling them. It seems like the Dragon Mother is just hoping for the best without really being involved in some sort of training.