Have heard of sibling jealousy but my 4 yr old boy is sometimes jealous of mommy kissing dad in front of him...how do you assure the kid?

I have a 7 year old daughter and a 7 month old son. At first, she was pretty jealous and often remarked that her brother was taking me away from her or if I am always playing with him instead of her. What I did was to make her involve whenever I am with my son. If I am diaper changing, she helps me take the new diapers & toiletries and helps me distract him while I change him. If she leaves for school or comes back from school, it's a routine for her to kiss him goodbye/hello irregardless if he's awake or not. And I often get her to look after her brother while I do other house chores. After a while, she became very very fond of him and would even order me not to make him laugh because only she can