Some quick thoughts: 1) Are other devices able to successfully connect to your Wi-Fi, and are they working/at speed? 2) What OS are you running? 3) Recent updates/upgrade of any kind? Successful, and did wireless work after the updates/upgrade? 4) If it's on some flavor of Windows, are all Windows updates (successfully) applied? 5) This issue still persists after you've rebooted/restarted? 6) Any luck running the network troubleshooter (again, assuming Windows OS)? 7) If she needs to connect/get some work done now, do you have an option to connect with ethernet (wired) as short-term while figure this out? 8) Could be hardware defect. Obviously under warranty. Direct purchase through Dell? Thru local retailer? What kind of warranty service came with it? Onsite? Have you talked to warranty support to see if they are any use in trouble shooting? Hope this helps, or at least gets you moving towards solution. 
Just purchased my daughter an Inspirion 7352 on July 31st of this year.  Initially worked great connecting to Wi-Fi but last couple of weeks get limited access and not connected.  She needs this for on-line college.  Any help would be greatly appreciated.
limited wifi