Dang $250. Even my first car back in 2004 was slightly over $250/mo.

Now if someone is putting down a large down payment or stretching out the term then the monthly payment amount is meaningless.

I get the idea and see why many people don't value a car anymore than getting from point A to point B but man $250/mo in 2023 is crazy low.

The simplest way of putting it is that you will be financially responsible for everything your sister is responsible for but without the benefit of actually living there.

As someone else already said, if you ever have to sign documents attesting to your financial obligations/debts, this counts.

You say you aren't worried about your sister not paying. I mean it's not a problem until it's a problem.

Many people cosign for others every day. Some people have a smooth experience and others get screwed ponying up the money for someone else.

If you don't do anything then it won't hurt them

Being added as an authorized user gives you all the benefits and none of the risks.

When you are taken off though that history also drops off.

Adding someone on it's own doesn't harm their credit but allowing someone to make purchases could if paying the bills becomes an issue for them.