Toddler is a bitter now😤

How can I get my 2 year old to stop Biting my 7 month old son? I went to the store and my husband was supposed to watch them but when I came back he had 3 bite marks on his (my son’s) forehead, chest and leg. I was so angry at my husband obviously and my daughter. She never bit anyone until recently. What do I do about the bite marks and how do I get her to stop? 😤 I already spanked her and showed her the marks she made.