When my kids were that age (and younger), they didn't seem bothered by the noise.
But why not take the extra precaution. Just because you're OK now doesn't mean damage hasn't been done.
Maybe cut out some felt or other soft fabric and glue the to some earmuffs and tell her they are her "puppy ears".
Maybe one of those wide head bands that women wear in wintertime. I know that sounds crazy at the river but if it blocks some sound is on just while the motors
running.

I don't know, just some ideas. But I think she would be OK.
Let us know what you try and what works.
Because you're dealing with a 2 year old girl, I guess I should say let us know what doesn't work

Good Luck.