Whenever you upgrade an armor piece, Sagheera will have it ready for pickup after the next Conquest tally. She will only upgrade one armor piece per Conquest tally period.
In order to "purchase" items from her with Ancient Beastcoins, you must have access to Sea. When you talk to her, she will have an option to "Ask about ancient beastcoins." Here she will detail what you can purchase and for how many Ancient Beastcoins. Once you have traded her enough Ancient Beastcoins you can choose to receive the item you want. Here is a list: