How do I push to GitHub under a different username?

A friend and myself are sharing my computer. I've made pushes to GitHub using the git bash shell on Windows 7. Now we're in a different project on that computer and I need her to push to her account. But it keeps trying to use my username and saying I don't have access to her repository:

$ git push her_github_repository our_branch
ERROR: Permission to her_username/repository.git denied to my_username.
fatal: The remote end hung up unexpectedly

This worked for me, it will prompt for username and password

git config --local credential.helper ""
git push origin master

If you use different windows user, your SSH key and git settings will be independent.

If this is not an option for you, then your friend should add your SSH key to her Github account.

Although, previous solution will keep you pushing as yourself, but it will allow you to push into her repo. If you don't want this and work in different folder on the same pc, you can setup username and email locally inside a folder with git by removing -g flag of the config command:

git config user.name her_username
git config user.email her_email

Alternatively, if you push over https protocol, Github will prompt for username/password every time (unless you use a password manager).