I find your emphasis on LICENSED contractors interesting. Most likely it was a "LICENSED" contractor who installed the plumbing in the first place. Prehaps she should get a recomendation and quote from him to fix the problem??
: Can you see the lettering that the manufacturer puts on the copper pipe when it is made? Is it type L or is it soft copper. Is it larger than 1/2 inch diameter? If you hold the copper pipe in two hands three feet apart, is it flexible and bending easy? Is so the pipe type used for the house might be soft copper and not hardened enough for the well water. If the pitting that is inside the pipe is continuing, and is chemical related, you will notice discolorations inside the cut out section that indicate copper ion oxidation. You could take the pipe section to a laboratory and ask for it to be analyzed. You could much more easily ask for a LICENSED plumbing contractor or two or three, to come over, and recommend a solution to let you sleep. The original contractor has been paid for the job, it's out of warrantee, and won't have any source of income to just apply bandages here and there. The Real Estate agent has been paid, and won't find a reason to be much help. If two or three LICENSED plumbers establish an idea that the cold water pipe ground for the electrical house supply is eating up your copper pipe, and the whole house now needs to be re-piped, the homeowners insurance policy will cove the cost of your temporary housing and replacement of the pipe, as well as an electrical ground separated and isolated from the cold water pipe ground, as well as a follow up inspection and warrantee to allow you to sleep.
: : We moved into a new house 1 1/2 years ago. House is on a well system. Had the water checked by Culligan, no issues. Water piping is all copper. 6 weeks ago a leak developed in a run of pipe, then stopped after 2 weeks. Last week another leak developed in the same pipe. Plumbing co. that installed the original piping replaced a section of pipe, said it was all pitted on the inside, took a water sample and said possibly ph level too low or an electrical grounding problem. Tonight I found another leak 20' from the original one, same type in a straight line of pipe. Have you ever heard of this happening in a new house? Would sure appreciate some help, I'm not sleeping. Thanks, Mike.