Answer:
My mom was so proud of me.
Step-by-step explanation:
The original sentence is -
My mom was so happy for me.
Now, to add the word "proud" in the sentence, we cannot just put it in between any of the words or it will result in the formation of a new senseless sentence. And, in order for the word "proud" to be correctly used to make a meaningful sentence, we have to replace some word/ words. Also, the tense of the word "pride" is a noun or verb that cannot be really coordinated with the other words in the sentence. So, to make a meaningful sentence, the word 'pride' has to be changed into the adjective "proud'.
Thus, the final and new sentence will be-
My mom was so proud of me.