A woman who gives charity from food she prepared without spoiling it will receive reward for her giving, as will her husband for earning the money, and the storekeeper for selling the ingredients. The rewards of each person are separate and will not decrease the others.

2.  Narrated 'Aisha: Allah's Apostle said, "When a woman
gives in charity some of the foodstuff without spoiling
it, she will receive the reward for what she has spent,
and her husband will receive the reward because of his
earning, and the storekeeper will also have a reward
similar to it. The reward of one will not decrease the
reward of the others. "
(Sahih Al-Bukhari, Vol. 2, Hadith 506)