Reading your post, this popped into my mind.
“Wherever you may be, let your wind blow free; whether in church or chapel, let it rattle.”
I know it’s a different bodily function, but noise is noise.
Maybe your friend can’t control her sneezes. Unless, she’s just used to doing them one way that anything else genuinely is difficult.
I can control mine, and I have two types: the dainty, for when I’m with company, and the ‘let it free’ variety which goes something like, Waaa-hooo! Boy, I love it! Like a release of tension.
The poor French bloke beside The Seine didn’t think so though. I didn’t know he was there till he turned round from putting something in the back of his van, saying, “Oooooooh.”