My sister says her laptop wont be able to connect to the router if the ssid is hidden or something like that...
?
You will need to set something on the laptop that says "Connect even if network is not broadcasting" or something to that effect. Try under Network Connections.
That's not good, because if you go to a wireless hotspot, and your home AP is called Linksys, every Linksys router in the area with the same SSID will become a target for the laptop to connect to at the hotspot, therefore compromising your security, because not only can hackers watch your tracks, but you think you're connected to a secure (but unprotected) network, when in fact you are connected to a similar unprotected AP which hackers can gain access to.