Which macronutrients and micronutrients are those?
Plant provide, but less efficiently: iron, zinc, choline, calcium (some tofu provides, but depends on coagulant used), iodine.
On the flip side, plants provide fiber and numerous phytochemicals that meat, fish, and eggs lack.
Irrelevant amounts come from diet, adequate amounts come from sun exposure. Everyone should be supplementing this.
>Taurine, creatine, Carnosine
Irrelevant, synthesized by the human body.
>Retinol
Best consumed from carrots, sweet potatoes, etc. Only relevant animal source is organ meat (liver), which most people aren't consuming.
>B12
Even meat lovers get deficient on this, dietary intakes are usually inadequate. My mother and sister are rabid meat eaters and supplement it, everyone who has the means to should.
Anecdotally, my sister in law has been vegetarian for over a decade and just recently been diagnosed with anemia.
Also your sister in law hasn't been well informed - it's a known fact that vegetarian diets have less iron in them, and women especially should take an iron supplement because of menstruation combined with the diet. But it's just one pill.