wife is a cheater...best way to get into her email acct

[slim]

so wife has admitted to a 2 yr affair. What is the best way to break into her Yahoo acct? If I just keep guessing her password, will Yahoo tell her about the attempts?
I know nothing about keyloggers but she only accesses her email through her laptop which has fingerprint security to access her computer. So even if I knew how to use a keylo, that wouldn't work right?