Following up on an email to a potential adviser for feedback on research proposal?
When to email somebody a follow-up email depends on how time-sensitive the topic is and other factors you may be aware of.  For people in close contact (e.g. a student taking a professor's class, or colleagues), a day or two is typically an acceptable wait time. For somebody that you initiate email contact with, a week is more typical. Other considerations are how much thinking the response might require: if you asked lots of questions, they may need more time to think about it before formulating a reply. Do you have reason to believe the person may be busier than usual (e.g. exam season or a conference)? If so, it would be polite to give them more time to catch up with their email. 

In this case, a week or two is probably a sufficient amount of time. Less than a week would be too soon, as you haven't met them before emailing them. More than two weeks is getting close to winter break, at which point most academics check their email less frequently, and you need enough time to contact other professors if she suggests any. It's also possible other people are asking her similar questions. It's a busy time of year, so one follow-up couldn't hurt. (If she doesn't respond after a second email, I wouldn't send a third email.) 

Here are a few resources you could check out about how to write your follow-up email: 


How to write a polite reminder email? 
How to remind a professor about sending papers to read?


You'll find other resources linked from these questions and by searching online, too. Most formal reminder emails follow a similar format. Remember to be brief. 

It's certainly worth contacting other professors! I do not see any reason why not to.