All words can be used except for "eres". If the person just meet her stepmother and she got a bad vibe it would be "sea". If the person hasn't meet her but is assuming her step mother is a bad person then it would be "sera". Lastly when using the word "es" in this entence it would be like affirming that she is indeed a bad person.
Habia because Habia means there were. On the other hand we have contaba which men tell, saludaba which mean said hi, and nacia which means born. so your best bet is Habia
