College faculty are very accustomed to writing letters of recommendations for jobs, graduate school, med school, etc. But they are also chronically overwhelmed with such requests and notoriously slow about responding. If you are confident that she knows who you are and you did well in the class, then I wouldn't fret too much about a week passing without a response. Just email her again asking if she got the email--or visit her office hours and ask in person. Best case, she will apologize for the delayed response and agree to write a letter. Worst case, she will ignore you or say she's not sure she can speak that well to your strengths or some other code that she doesn't want to write a letter for you. But I assure you that if she likes you and would write a good letter for you, she will NOT change her mind and refuse to do so just because you followup on your initial email. Remember that she may very well get dozens of emails a day from students.
Finally, one piece of advice I always give is to subtly ask faculty if they can write you a POSITIVE letter of recommendation. By that I mean to say something like this, "Dr. X, would you mind writing me a positive letter of recommendation for medical school?"
It's a lot harder to lie to someone and say, "Yeah, sure, no problem," when they know they really don't think that highly of you and cannot write a truly positive letter of recommendation. You want good letters of recommendation--not just letters saying, "Yeah, this person was in my class."
Good luck!
