Question

I urgently need help with a couple of sentences. Can you also check my previous post. I need to prepare the letter for tomorrow. Thank you.

1) The lady at the bottom left of the photo (is "in" the bottom a mistake when describing a photo?)
2) How long is it since you knew Peter?
(Wrong: I believe the only possible sentence is: How long have you known Peter?)
3) She is wearing a jacket with a long silk dress under it (underneath is a mistake?)