Hey Marion!
That's a simple thing to do:
You need to expand your WLAN. This can be done in 2 ways:
- First you can set up a repeater. This one receives the signal from your router and transmits it again. Easy to install, but it slows down the traffic for the expanded area.
- Second is to set up a directed transmission to your sisters house. This can be done by special antennas.
Check out the usual manufactures and search for "RangeBooster" and "Repeater".
Check these:
Dlink products They have pretty cool products, I use them most times I get to set up some network.
regards
Torsten