Well if you lose enough/they win enough, you end up with all the smurfs above you and then you're free to learn and have your mmr adjust appropriately in line with your skill. Occasionally rather bad players make smurf accounts for reasons, so you might even find that you're playing with/against a smurf and doing just fine.
I also feel like getting completely rekt by better players is a good if harsh way to learn. Basic mechanics you can get from bot games, but really learning whats possible is best learned from players who have it mostly figured out. Otherwise you might find yourself picking up bad habits that work fine against clueless players, but as soon as you come up against good players (smurfs or otherwise), then you get destroyed and might be even more confused as to why something that'd always worked for you isn't working.
Another thing with newer accounts is it isn't necessarily as obvious as it might seem as to who is a smurf and who is just someone who just happened to figure out their champ decently and snowballed off of it.
Also, if you're staying under your tower when your opponent is capable of all-inning you, then you're probably already better than a lot of bronze players. Riven is a snowbally champ who basically relies on an early all-in and then repeatedly killing you, so if you're helplessly farming under tower, then you're basically doing the right thing there. She'll be kill starved and you'll probably outscale her, plus since she has you pushed to tower she's subject to jungle ganks (which probably aren't a thing until 20+ or so realisticly, but maybe you'll have a friendly jg main smurf who'll adopt that role early on).
