Friend is returning after not playing for ~12 years. How do we stop facing Plat+ players?

Basically title.

Convinced friend to come play after not having played since like S1 or S2. We're about 35-40 games in and still consistently facing Plat people, even when she solo queues. Is there a quick and easy way to get her MMR/Elo to where it should be? (Bronze-ish)

Should she try playing some ranked and getting a low rank? What are we missing?

Edit: I should note, she's playing on her old account she made back then.