No wi-fi signal in daughter's bedroom from uverse router 3801HGV

Hello  I was a uverse customer at one time but has switched due to personal reasons.  Anyway, we still have the router 3801HGV for our DSL services.  I have a laptop and wireless printer/scanner/fax all in the same room.  I have access to wireless into the living room, intermitant in my room, but my daughter's room, we have no wi-fi access at all!!  The house is set up like a u-shape....so router on one side of house and kids rooms & mine are on the otherside.  The signal is very weak or just none at all.  Daughter has to come to this side of the house to use her iPhone.  We are thinking about an iPad for school but dont want to spend the money if she cannot access wi-fi from her room to do her homework.  She has to sit at the kitchen table with the laptop since this is the half way point to pick up the signal.  We bought a AV wrieless extender and plugged in into the wall in the living room, it worked for one day then it stopped, so we thought "get a better one".  Bought a Cisco Linksys N300 and have to use it on the wireless laptop with CD in order to install it(strange).  I have tried to use the CD to set up but it asks for our network password...which I have put in the wireless network key that we use for everything wireless in our house, but that is not what they are looking for.   There is NO code from the Cisco router to use (which I know most come with a card that has all that info on it).  Nothing seemed to work.  Any suggestions or help??? Trying to get wi-fi access in daughters room and not sure how to achieve that.   Thanks!!