People can become irrational and a little crazy, especially when they are dealing with something they are emotionally invested in. I don't know what this person's situation is, but I'm willing to bet that her response is based on something else going on in her life and your offer was the trigger that set her off. In my day job I negotiate with people every day. If negotiations become emotional I tell them that my offer is based on pricing of alternative products in the market and that my price is just my opinion of what the value of their product is. This way you bring it back to value of the product and not value of the person behind the product. I would not apologize because then you are putting feelings back into negotiations and you are keeping the seller tied to her emotions. You need to keep the attention where it belongs, on the product.
