There's something very wrong there Kay. The Strelitzia shouldn't lose
its leaves like that. First thoughts are damage to the root system
either through over-watering (possible after a re-pot), physical
damage or infestation with root mealybug or vine weevil. The plant
should be carefully knocked out of its pot and the roots inspected.
Healthy roots are plump and white or creamy white. If over-watering
is the problem, the compost will be sodden and the roots will be brown
and rotting. A complete repot into fresh, sharply drained compost
followed by watering only when the compost has dried out will
encourage fresh roots to develop.

Root mealybug will be apparent by the mass of white waxy fibres around
the roots and on the insdes of the pot. Close inspection will reveal
the adults up to 3mm. long on and around the roots. Most on here will
be familiar with the larvae of the vine weevil and damage caused
exhibits as roots eaten through right into the base of the plant.
Drenching the roots with a solution of Provado will deal with the
pests and subsequent careful watering will encourage fresh root
growth. I've only seen vine weevil in Strelitzias grown in soil-less
composts - plants grown in the preferred loam-based, gritty composts
seem relatively problem free.