Is she related to "you know who" ?

Nope but her mom is Rosemary Harris, the well known theatre actress. Jennifer looks a lot like Rosemary who also resembles or resembled Streep when she was younger. They both have those incredibly high cheekbones like Streep does.

I wondered the same thing.

I just found out she wasn't. I don't know why I thought she was. I could've sworn someone told me that. Maybe they did and just confused them.

I thought the very same thing. A young Meryl from her Kramer v. Kramer days.