Question
my wife has been diagnosed with planter facietis.  one doctor said hot and  another doctor said ice.  which is correct?  

Answer
 I doubt either would really help much, you can try both (not at the same time) and see what makes it feel better.  Theoretically, heat is the correct answer, because it would tend to relax the plantar fascia, and that should make it feel better.  Cold also gets rid of pain, so either one should make it feel better.  It would only be a short term solution.
 My approach (assuming the diagnosis is correct) would be:

1. Steroid injections (or oral Non-steroidal anti-inflammatories)
2. heel cups for temporary releif and custom made orthotics for long term relief.
3. Possibly taping of the foot for a week or two if it is very painful.
4. Physical therapy / stretching
5. IF the above doesn't work, then possibly surgery