2.5yo started hitting 7months old younger brother

My 2.5yo started hitting her 7months old younger brother whenever she is unhappy with him. Any other parents experienced this & any advice to discipline her? Tried to explain to her that we need to sayang instead of hit & brother will feel pain pain. Do i need to spend more quality time with her to make her feel loved? Did she reacted that way because i spend lesser time with her? I hope she will stop hitting her brother before he starts to learn & hit her back too 😪