dnd 5e: How can I as a DM make a low level melee rogue feel useful in combat when the party doesn't have a tank to trigger a sneak attack for her?


For Druid + Rogue at level 1; Combat is not necessarily necessary.

Focusing on the rogue's DPR is, IMO, you as a DM watching this party through a very narrow lens. I suggest that since (1) you only have two players, and (2) neither of them is of a warrior archetype, the adventures you run through them until they reach the second level should focus more on role play, exploration and evasion / mobility and slightly less in close combat. But when they opt for close combat, they need to try to compromise on their own terms. (Credit: Sun Tzu theory)

Why?

In the world, in a narrative sense, the odds of a rogue and a druid going and mingling in the dark hallways of an underground dungeon are not very high. And, crafting the adventures as suggested you make them work as a team From the beginning. Beyond that, they may not need a tank to create advantage.

How can the druid help the rogue gain an advantage?

Occasionally, with the Help action, but does the Druid player accept that? Maybe and maybe not, but in any case that's between the two players to discover. They need to work as a team. because there are only two of them.

In some situations, it helps will be be a good use of an action, in others it will not. Let them solve that by playing and making decisions / choices.

Some druid spells can offer an advantage. Again, are your players those who need to work as a team to make the most of this.

  1. Tangle (SRD p. 140)
    Note that a creature that fails its salvation is

    restrained through the tangled plants until the spell ends.

    From Appendix A, conditions, restricted

    Attack rolls against the creature have an advantage, and the creature
    Attack rolls have a disadvantage.

    The rogue attack with advantage allows a sneak attack.

  2. Fairy fire (SRD p. 141)

    Any attack roll against an affected creature or object has an advantage if the attacker can see it, and the affected creature or object cannot benefit from being invisible.

    Rogue has the advantage, sneak attack.

It is okay to train your players if they are new; you are the DM, coaching is part of your role.

Change your DM paradigm to suit your two player group

Your first level of adventure needs empathizing using your wits, not physical strength, to achieve your goals. Between the druid's spells and the rogue's ability to succeed in skill tests, and stealth, and occasionally applying a sneak attack if someone gets on the druid's grill, you can have some exciting and challenging adventures without a tank.

At level 2 Rogue gets cunning actionDruid gets wild way; Your options expand significantly.

Experience:
Two of us played a two-rogue party for one session (urban setting) to help a DM get used to running a game. We use ranged attacks, movement and anything but melee combat to achieve our goals. It's doable, it's fun, and it's still dangerous for the PC.