I'd go for the higher privacy screens within your own boundary. Get a car junk yard to store some old crushed car bodies on piled high on top of each other for 3-6 months to create the screen. They will be au fait with safely securing them. They may even pay for the temporary space leaving you with enough money to later build a truly aesthetically pleasing barrier, something like that big reflective glass barrier to her if she doesn't move! Hopefully she will decide to move when that is all she can see. My dad actually used this strategy successfully with a problem neighbour in the past! Meanwhile have a chat to a lawyer. We have one of those problem neighbours who complains about (non) barking dogs and gets her kicks by watching us put out washing. She now looks onto my chicken coop and thought it was a dog kennel. It makes me feel like going naked when I tend the chickens to give her something to really scare her and having a heavy metal rock band rehearse regularly in my garage. It is horrible to be overlooked by a neighbour who is so problematic and likes to use your family as her reality television set! Do check with a lawyer about her possible trespass onto your property. My guess is she used Round Up on a windy day!

Not sure how it would go in Brisbane but what about trying a conifer? They grow fast and very tall. You can shape them or leave them natural. They are plain and certainly not tropical. Maybe speak to a local nursery and find out if they would grow in the sub-tropical climate of Brisbane first, as they are usually in colder climates (Sydney and south). Leightons Green Conifer – Leyland Cypress http://www.evergreengrowers.com.au/shop/hedging-screening/leightons-green-conifer-leyland-cypress/ Your quite limited if there's not enough sun and you dont use bamboo or tropical plants. Many other screening plants or hedges wont get tall enough for that space and climate. I hope you find something.

For low maintenance in such a variable climate while preserving light access I think I'd go for some kind of a translucent decorative screen, with maybe just a few potted plants to provide some greenery. If they're not planted in the ground you'll have to be even more careful to ensure they get enough water. Or, thinking further, I've seen Chinese star jasmine used in challenging commercial locations, including as a screen around a cafe's outdoor area, it looks amazing and appears to be very hardy and copes with a temperature range similar to yours. Two drawbacks though, some people dislike the smell and it needs pruning so not low maintenance. It's difficult finding something that ticks all the boxes.

Pittosporum is very quick growing and has a narrow trunk and thin branches so its probably the best option if you want a tall and dense, but also thin hedge - I have Silver Sheen as a hedge in several areas in my yard and it grew from 1 foot high to over 2m in 2 years. Alternatively clumping bamboo (not as invasive but probably best planted in long containers and placed along the fence line) will quickly give you privacy and both the leaves and trunks of bamboo are attractive. If you go for one of the Lilly Pilly hedges Id recommend one that doesnt fruit as much, as the berries can make a big mess especially when the birds notice them.