Was wondering how women dress for restaurants. Are slacks and a top okay? Jeans and a shirt? Or do people get dressed up? I know most places are more casual nowadays.

You can dress anyway you like. If it is an upscale place most likely women will dress more elegantly. But chance are that any given day there will be a bit of everything.
In general Argentine women pay a lot of attention to fashion and dressing well.
To make it short think of New YOrk.

We spent a week in BA and as the previous post said you can dress anyways you want. We ate in very nice restaurants and some local ones. Never had a bad meal. Slacks and sports shirts for men, dressy tops for women and you can't go wrong.

I agree with arbegold. My husband packed a sports coat as La Bourgogne said jackets required. He followed directions at that restaurant to find only about half the men wore jackets. He never wore it again.

I wore black pants, nice tops and sometimes a blazer and felt appropriately dressed. I didn't notice many in jeans except on young people.

I agree. I wore black slacks and tops/shirts/sweaters and was always comfortable. There are some restaurants that you can get away with less, of course, but I never felt underdressed - which is more of a faux-pas in my opinion!
Basically, that is what I wore the whole time in BA. You will see jeans during the day, but more women will be dressed in slacks.