Ответ: Did she feel well on Monday? No, she didn't. She felt ill.
Составляем вопрос, используя вспомогательный глагол Did для прошедшего времени (Past Simple) и информацию из условия: feel well / on Monday.
Did she feel well on Monday?
Отвечаем отрицательно, используя no/ill из условия. Составляем отрицательный ответ: No, she didn't. She felt ill.
Ответ: Did she feel well on Monday? No, she didn't. She felt ill.