I've been playing this game since 2.0 release, and late this year much like yourself I decided to introduce my SO to the game, it was her first MMO of it's kind and she was freshly level 50 when we ran Praetorium.

We had a similar experience as you, however, we managed to keep up relatively well with the pack up and around until the mech portion of the duty, where we got left behind, it was only by the time the party engaged Nero that we could help again. Unlike your experience however, no one blamed us, and I don't think people blaming new tanks for something like that is a very common experience, it just seems to be Praetorium that's ran with this 'speedrunners' efficiency. I think mostly due to the duty's length compared to others. The best advice I could truly offer, if you and your girlfriend ever do decide to come back to the game, is in such cases as Praetorium, wait for the team to clear until the duty's boss, where anyone left behind will be offered opportunity to teleport directly to the fight. Not ideal, by any means, but Praetorium is just one of those old pieces of content no one seems to enjoy taking their time with if they can help it, and while their way of doing it impacted your experience, their way isn't a strictly wrong way to play, either.

If you move on to new games, I hope you have a better time, if not then I'm relatively certain the experience was likely a unique enough one that it won't repeat that commonly, from my experience.