I'm not sure I understand that question. The adjective has to agree with the noun in number , case and gender, and there are three genders (masculine, feminine, neuter). And then there are several different "declensions" of both nouns and adjectives, which are the different patterns of ending---she's probably come across three of those, too. All of these examples have the -is ending for their genitive, which makes them "third declension". She should have a table of examples of what happens to third declension adjectives when they're paired with nouns in each of the different numbers, cases and genders.
I was made to learn the tables by rote:
"Brevis brevis breve, brevis brevis breve, brevem brevem breve, brevis brevis brevis, brevi brevi brevi, breve breve breve;
Breves breves brevia, breves breves brevia, breves breves brevia, brevium brevium brevium, brevibus brevibus brevibus, brevibus brevibus brevibus". And breathe.