Q: does router location affect my daughter's mini's  wifi?

The distance between the Mini and the router effects the wifi connection.

So does what is between the Mini and the router.

Also, interference from other routers and other devices affect the connection.

AirPort and Bluetooth: Potential sources of wireless interference

As already stated, distance and what is between will

have an effect. 

The interference issue can have a signifigant effect

if you live in a fairly dense populated area with many

people with their own WiFi.  If this is the case, you

may need to force the selection of channel for WiFi

communication.  If this is the case, you would need

to set up your wireless router to use a different channel.