Colleen,
Even basic PS status will give you tel. support. Give them a call as sometimes they can be quite helpful.
I spent 15 minutes on the phone last week re. a buyer who kept harassing me with emails, leaving derogatory FB for me and my competitors and ten minutes after I hung up, the guy was turfed off the site, NARU. (OK, now he has filed multiple Paypal claims - fraudulently, and will likely lose his PP account over it).
I am really unclear as to what your seller is complaining about. We have bought large inventories of items and are selling them at up to 30x the cost, let alone 3x. It's called business. Personally, I am always happy when my competition buys from me and lists at a higher price:-)
Yes, you should have read the signs but, you know what? Been there done that myself more than once LOL!
You might be best off to let her file the "unpaid" disputes and respond factually (combined shipping). Then, phone trust and safety and have the strikes removed.
If you get the right person, they will help you. After my guy was NARU's I phoned again and asked that certain FB be removed and other FB I wanted left there (he bought over 50 items and left some good and some bad FB). They obliged, believe it or not.
I even asked them to remove some FB (bad FB) from my competitors and let the good FB stand. They again obliged.
On occasion, I have found PS support to be quite understanding so phone them and calmly state the facts.
Good luck!
Xena