It would help if we had the original ebay links to the items you bought.
Also for future ebaying, when negotiating combined shipping, you can always request a lower shipping charge. Some sellers are hard a$$%%^ about their terms but most are compliant with options. Keep in mind that if shipping through usps like it sounds like she is doing, usps has done away with the parcel post option over a certain dimension. Since we dont know how big the box is we cant assume to know if parcel was even an option based on the shipping box size.
Alot of collectors like to keep the boxes themselves in as pristine condition as possible so maybe she overcompensated the packing materials. Also, packing materials can add considerable weight, especially if using cardboard pieces to help with any possible crushing during shipping. Plus she might have added a cost for those materials and her time to find a box big enough for combined, and her time to do all that is necessary. Some sellers add handling and some dont.
But having the original links to the buys on ebay would help with these assumptions. For $2 more its not too bad, it can be hard to calculate shipping, however, as a seller myself, I wouldnt have asked for that difference because Im worried about my DSRs, which you can ding which significantly hurts the seller.
Or you can ask her to refund you if you feel that the shipping is more than you reasonably expected to pay. I know usps raised their rates again recently. Dont mention dinging the DSRs and see what she does. If she refuses, gives a hard time ect, then ding her stars on shipping cost,when leaving feedback. Really do ask her first because the star system hurts a sellers ability to sell if they get too many bad stars and can be banned permanently.