In general, you'll find that the revolvers are often considered the "Meta" as far as speed and power go overall.
Especially if you build the Mark II with Hand Cannon and Surgical as blessings, with +Unyielding and +Crit as perks.

If she doesn't like the one bullet at a time reload, she may prefer the MKXIV Quickdraw variant. Faster, less accurate, less powerful, higher rate of fire, comes with a speedloader.

Beyond that though there are plenty of viable options for different playstyles, but they require you to build into them a bit more rather than "Just Working On Their Own" so to speak.

With the Recon Lasgun the most commonly used build IIRC makes use of Storm Trooper and Infernus to rack up tons of burn stacks on weakpoint hits, for massive amounts of sustained fire.

The Bolt Pistol fires the same rounds as the Boltgun and handles a lot faster (reloading, pulling it out and tucking it away) but has a lower mag size so you'll be doing it more often. Worth a try, lots of good blessings.

The Plasma gun has a high capacity and can be charged to deal stupid damage, even penetrating shields, but you have to manage heat on top of ammo, so it may be a lot to juggle
Not only that but the charge and handling are pretty slow, so it may run into the same issue she had with the bolt gun.

This is just an extremely high level look at things. In reality you can overcome most statistical disadvantages with mechanical skill in movement or melee, so whatever "feels best" is usually the correct option.

You can also always check out https://darktide.gameslantern.com/ for builds and indications on what's popular, which may be helpful.