water damaged wifi card

My daughter spilled water on her Macbook Air keyboard last September right before heading back to college. Everything works fine except for the wifi. The message comes up saying that the wifi card is not installed (something like that). We took it to the Genius Bar and they found out it was water damaged, not covered by Applecare, and it would be very expensive to repair. She has been tethering her phone to the laptop in order to use the internet and it has worked fine. However this month I had a large data overage charge on my phone bill. I am looking for other workarounds for this problem besides tethering the phone. Anyone?