Unless your teacher specifically said, "no help allowed" then it is expected that you use a dictionary, computer spell checker, and another person to proof read your work. It's called using resources. The only other exception might be working on a "take home test."
It's even better that your friend explains the reasons for making the changes. If your friend does that, she's really being a tutor for you.
Reading out loud is one way for people to "hear" if their word choices "sound" right. If you can't hear, then you can use another person's "ears" to critique your writing.
Finally, if it really bothers, you speak privately and honestly to your instructor about this. She makes the final decision about it. If your instructor is fine with this arrangement, then it's no one else's business.
