Cant access the rest of her shop menu to complete the mission because I already owned the top set.wont let me get into the menu to scroll down for the rest of the knowledge she sells.

If I understood you correctly, this is not a bug but the quest is a bit misleading since the marker takes you to the vendor - the books you need are actually in the bookshelves around the library, I was wondering about this myself for a while but the quest description actually tells you to look for them in the shelves.