Hey, Javi. In English, this grammar describes feelings. There are two ways to use it.
1) She is frustrating me. --> The feeling is frustrate and it is your feeling. Me is not needed but makes it clear it is your feeling. If you change me to him or a name then it is that person's feeling. She = the reason for the feeling. The 'ing' makes the subject of the sentence the reason.
2) I am frustrated by her. ---> You are now describing your feeling or subject's feeling (ex. He is frustrated by her.) 'By' shows the reason for the feeling this time.
There are some words that don't follow these rules like scare and impress. ex) 1. Scary, 2. Scared / 1. Impressive, 2. Impressed. I hope that helps.