It would be nice and convenient if this were true, however I don't actually know if she did or didn't get such a vaccine in childhood and in any case it would seem that it is not something that lasts a lifetime and would indeed need to be refreshed in this instance. It's true that asking everyone to get this vaccine prior to being in proximity to the new born isn't something that's enforceable or verifiable but my criteria for deciding whether or not to do this is based on the relative harm caused by our actions not our capacity to feign doing so and successfully get away with it. I don't want to be responsible for a child contracting a preventable disease because I was too afraid to bring up the issue, I just want to find the best way to raise the issue.

If I am not able to convince her, I may have no choice but to decline the invitation, which will put me in the oh-so lovely position of having to both deal with the fallout of the unsuccessful attempt to have my wife reconsider her refusal and any resentment that might cause, plus a continuing multi-year long schism between my family life and my marriage as we remain unable to attend any events together where the child is present until such time as the kid themselves can be vaccinated.