Airport extreme as wireless repeater

How do i set up airport extreme to be repeater of my nearest AP ?

Sorry, but Apple uses proprietary settings that will only allow an AirPort to wirelessly extend the signal from another Apple AirPort router. The AirPort router will not be able to wirelessly extend the signal from an Asus router.

If you cannot run the Ethernet cable, take a look at a pair of Ethernet over powerline adapters to try to send a signal over the existing AC wiring in your home. The theory with these devices is that you already have the wiring in place.....you just need the adapters.

Any computer / electronics superstore will have a selection of adapters from which to choose.

As per Bob's comments.

But if the Aunt is living in separate granny flat or house next door.. you will need to use wireless repeater of some sort or wireless bridge.

If you get decent wireless signal at your Aunt's, then you can use any standard wireless repeater with ethernet to create a wireless bridge. Another Asus of course would be the ideal but it isn't strictly necessary.

The only Apple router that can manage it is airport express.. which can act as wireless bridge (apple call it client mode). That will then plug into the Aunt's Extreme.. although perhaps that isn't really necessary unless she is using it as Time Machine backup with USB drive etc.