There are several types of caveat available to be lodged in Queensland: 'consent', 'lapsing', Registrar or court ordered. The last two don't sound relevant to your situation.
Any caveat which is lodged must be in respect of an identified interest in the land. If this is insufficient, the Registrar of Titles may cancel it. The requisite interest in the land is required, even if the caveat is consented to by the owner.
A consent caveat means you have the written consent of the owner. This type of caveat remains on title. They are not available to equitable mortgagees.
A lapsing caveat is only temporary. Once lodged (if successful), you have a time period to start court proceedings to establish the interest in the property; either (a) 14 days if the property owner serves a notice on you requiring legal action be commenced, or (b) 3 months. After that, if no court proceedings have been commenced, the caveat automatically lapses and the Registrar of Titles may remove it.
You also only get one bite at it. Once a caveat has been lodged, a further caveat on the same/substantially the same grounds by the same person will likely be rejected.
So, even if you could argue you have an interest in the land - which I don't think you currently have - the best you can do without your mother's consent is a lapsing caveat.