Your friend is being silly.
Guess she still has some growing up to do!
If she's living her life, keeping busy, enjoying herself, then why isn't she proud about that instead of feigning shame over not being married w children.
She's not tied down, she can do as she pleases with nary a by-your-leave - and marriage/kids isn't for everyone - some people try it and really suck at it.
It's not everyone's cup of tea!
AND - most importantly - if your friend doesn't like a question - who says she HAS to answer it?
She doesn't owe ANYONE any explanations!
Side stepping a question can sometimes be an art form - politicians are experts at it.
She can say "No, that's too personal" or answer a question with a question or out right lie (who at this reunion will know any difference?) and tell a tall tale or obfuscate an answer that sounds satisfying yet conveys little or no actual information.