any help with this scenario?

Your original plot description made me think that the story would be obvious: the two would fall in love and live happily ever after. Although you may want that to be the eventual outcome, you do need to introduce lots of conflict preceding the happy ending -- if that is to be the finale. I realize that you understand the preceding as revealed by your asking the question with its several options. I do like the idea that she feels guilt for being attracted to a new man so soon after her husband's death, and I think, too, that the concept of the brother-in-law/sister-in-law's being horrified/upset by her potential new (secret?) relationship is an interesting sidetracking of the relationship. I think that you might have the pair become hopelessly attracted to each other despite multiple obstructions that endeavor to drive them apart. You could most likely employ several of your potential conflicts, including having the man involved in a long-standing relationship in which his significant other has expected for some time that they would marry. Such barriers to the prospective lovers' developing the lasting love affair which they yearn to do would make an intriguing plot, in my opinion. Why don't you try writing the story that way?

Maybe 1. That would pose a problem- she could be trying to escape her grief by throwing herself into something. The man notices this and stops her. She spends a few days away to work out how she's gonna sort it.

4 could be a cliche unless the sister-in-law seems to be doing it to honour her husband's memory but actually wants the guy herself. The woman is happy with the man and is about to run off with him when the sister-in-law stops her. The woman chides herself for being so ridiculous. The sister-in-law runs off with the guy.

Here's an idea you might grow something out of...

Don't bother encouraging her to be faithful to her husband's memory... she's over him or she isn't. But, she could grow closer to this new guy if, during their chat, she confesses how she lost her husband...i.e. they were supposed to be together...she was late...she still feels responsible....he wouldn't have died if she'd been there. Maybe the newbie tells her he is recently divorced and his wife and kids have moved to a foreign country.So they establish a common bond of loss....A few silent minutes pass and he asks are you hungry? I'm starving...she says me too and they walk to the market and buy fresh fruit and cheese for lunch. which she realizes is their first "non-date" date.

Sometimes the answer to literary questions stare the asker in the face. She is your creation; so put yourself in her position and do some role play. How would you react to certain situations that you put her in? At least that way you will never be at a loss to move your character and story forward. Good Luck with it.

she'd have to be overt for a shy guy. Women can grieve through sex with other people. just an idea.

Well I guess thats one way to write a book - get everyone else to do it for you!

Why dont YOU write it and post it to see what people think!

She should rape him, kill him, then rape his dead body.