It's impossible to know for sure without proof - either a detective, or cracking into her email account, but your gut is a good indicator. Either way, she isn't interested in acting in a way that provides safety for you, so it's a big red flag.
If you want to know for sure, install a keylogger on her computer. If she's in an A, she no doubt has a secret email account and you'll get your answer.
Do you guys live together? I couldn't tell from your post your sitch.
I don't care, then I do, then I don't, then I do... la de da
