Airport to hotel transfer in Venice

When you arrive into Venice Airport follow the signs for transportation and specifically the signs for water taxi. You’ll walk/ride moving walkways all the way to the dock where the private water taxis pickup and drop off. If your hotel is accessible from a canal and if the tides aren’t too high then the taxi can take you all the way to the hotel water taxi door of the hotel. Otherwise they’ll get you as close as possible and you’ll be required to walk the remaining distance.

Where is your hotel located and what is the name? A private water taxi should only be 115 EUR, way less than $240 US. You will have to make your own way to the water taxi dock, but they have a moving walkway for much of the way. Sounds a bit excessive if you ask me.
https://www.motoscafivenezia.it/it/

So the DIY version of a private transfer would be a water taxi for a much lower price and the moving walkways get you to where the taxis are. That sounds fine to me, not too complicated - thank you for suggesting. $240 seemed like a ridiculous price!

Do water taxis take CC or will I need cash to pay the taxi? Also is the price fixed or variable - our Hotel is on Calle Del Rosa just across the canal from Ca’D’Oro.

Since your mom is so young (just 75!) and your hotel is so convenient, if money is a concern then the bus from the arrival hall to P.le Roma and then an easy vaporetto ride down the Grand Canal can be done for very little money. Since you will be likely using vaporettos while you are there the only marginal cost will be the bus from the airport, which you can add to the vaporetto pass.

Are you sure about the address of your hotel? My tools don't come up with a Calle del Rosa; nor a della Rosa, nor a del or della Rossa in Venice.

If you are right about the general location then I expect that you will be reasonably close to either the San Stae or Rialto Mercato stops. There is a Fondamenta Rossa, but it is well into the island and well off the Grand Canal and I don't expect that it is what you mean.

If your hotel is the San Cassiano Ca' Favretto, it has its own water taxi dock so you can walk into the hotel from the water taxi.
You can purchase the water taxi ticket ahead at the website previously given. You will give them your flight number. They say they monitor incoming flights, so will know if it gets delayed.

If Sam is right - and well done Sam for finding that - the hotel website says it is a 5 minute walk from the San Stae vaporetto stop.

Reading about all transportation options in Venice here will give you a good overview.

https://quickvenice.com/transportation/index-transportation.htm