hey hey jmh
you have a few options to think about from budget to expensive, plus keeping track of your gang of 12. are they all adults or are there kids too? when is this trip/cruise, pack light and everyone in charge of own suitcases. using a vaporetto may not be worth it to fit all of your gang and luggage from your hotel to station, go in style and pay the extra for private water taxi
voyagerinfo.com
how to get from venice to trieste cruise port. lots of info and options
motoscafivenezia.com
private water taxi "more expensive/split cost". will need 2 boats with your group & luggage. we've used them 4 times, way to go.
rome2rio.com
look at transportation and options: bus & train (cost PP, discount for seniors 60+ and the number of passengers, time of journey, and how long is journey)
private transportation in a van, make sure it fits 12 of you and all your bags. make cost you up to $1000, remember they need to bring that van back to venice
flixbus.com
trenitalia.com
give herself time to shower, pack, breakfast, getting to train station, what will the crowds be like who knows?
you may want to buy a snack/lunch at station or on train or bus, whichever you choose.
so much to think about what's not only best, "cheapest" just to save money, more headaches and stress. what's a few more euros for comfort with what you've paid for this holiday
aloha