Social Dilemma - Should You Have to Hide Your Political Beliefs?

Today's social dilemma actually came from my niece who lives in California.  I want to give her some good advice, so I'm interested to hear what you think.  This is the situation.  My niece is a Democrat, so it's no surprise that she didn't vote for the current president.  The guy she is currently seeing feels pretty much the same, but his family is Republican and Trump supporters.   Over the weekend, she had dinner with her boyfriends family for the first time, and politics came up.  And while she tried to steer the conversation elsewhere, ultimately, when they asked her point blank about where she stood, she said she was not a fan of the current administration.   She was nice about it, but she expressed her opinions.  She said it was awkward for a bit, but that they moved onto other topics and everyone was cordial.  On the way home however, her boyfriend told her next time politics come up with his family, she needs to keep her opinions to herself, and either not say anything or just nod in agreement.  He said that's how he has dealt with his family his whole life.  She was not happy about it.   She really likes this guy, but in her soul, she knows she can't just be quiet or nod in agreement for something she doesn't agree with.  And I support her in that.  I think she should try to avoid politics if possible but if it does come up, to be honest.  And she needs to explain to her boyfriend how important that is to her.  What would you tell her to do?  Really looking for your help with this so I can give her some good advice.