My sister has an electric furnace... She came home the other day... It was 59 in the house. If she turned the thermostat up to 72.. the breaker in the electrical box would trip.. She slowly adjusted the temperature up by a few degrees at a time.. But next day she comes home and breaker has tripped again... What would the problem be ?

Electric heating elements sagging allowing a short circuit.
Defective sequencer (s) AKA element switches/controls
Internal wiring defective (burnt wire ends)
Weak or defective breakers