Don't argue with an "expert." She won't ever agree with you, no matter how thoughtfully you explain your parenting decisions. Just smile and thank her, with a response like "I know you mean well." Then blissfully do what DOES work for you.
Your cousin may suffer from foot-in-mouth disease. If you are still not comfortable and just can't let her comments roll off of you, or if she becomes even more intrusive, consider telling her that you've patiently taken in 7 bits of advice from her already today, and ask if she would be receptive from some from you. If she says no, then she's gotten the message. She'll probably have to be gracious and say yes, so you can suggest (in a polite and friendly voice, of course):
1. Unrequested advice is hard for anybody to hear. For example, are you comfortable hearing what I'm telling you?
2. When you are a guest in someone's home, discretion and tact help keep the hostess happy that you're here.
3. When you are interviewing for a job, discretion and tact will make you seem more mature and endowed with good judgement.
4. If you have suggestions about my parenting, please be aware that I will probably find them annoying. But maybe we can have conversations about what YOU learned in your studies and how they work with the kids you work with. THAT I can probably hear.
5. Got that?
Good luck. Some people just aren't very sensitive.