I know the US situation, not the Australian one, but in the 1920s you basically had a number of "not very good" but "not as bad as they would become in a few decades" treatment options. These included:

• Occupational/work therapy — in which patients would be made to do forms of labor (sometimes farming, sometimes manufacturing) because it was seen as giving their lives structure (and the by-products could be used by the hospital or sold)

• Hydrotherapy, which ranged from taking baths (not terrible) to being sprayed with water of varying temperatures (not great)

• Psychotherapy, which is to say, the "talking cure" — Freudian-influenced approaches that had varying degrees of effectiveness depending on why someone had been put into the hospital

• In some US hospitals, sterilization (vasectomy or salpingectomy) was considered a therapy at this time (based an obscure French theory), but this was an unusual way to think about it

• Electroshock therapy was possible in this time, though not as common as it would later be

Which would be used at their hospital? I have no idea. In the US, the hospital systems were at this time so decentralized that your treatment at one hospital might not look anything like your treatment at another.

And of course a great deal of time would not be spent with any particular kind of "therapy," just the day-to-day management of activities and people that takes place in any institution or hospital.

The first psychoactive medications did not come about until sometime after the 1920s (thorazine became popular in the 1940s). Lobotomy is also a later development. Insulin shock therapy was being researched around this time but would not become common until the 1940s. So in many ways being institutionalized in the 1920s is less of a horror-show than, say, the 1940s-1950s — their inability to do anything was actually a boon. (It is better to work on a farm than to be lobotomized.)