It depends on how you ask. ​ If you were to frame it as *"I know you don't like speaking and this will be nerve wracking for you, want me to do it for you?".* You can clearly tell this would put anyone down and make them feel inferior. (Not saying you would approach it like this). ​ Now say you approached it as: "*Hey, just reaching out to offer my support in case you feel you could use a hand for xyz presentation. I know you got this on your own, but if you feel like it's something you aren't comfortable with, I'd be more than glad to lend a hand!"* ​ Just my 2 cents.