When to initiate contact...

Hi there, I'm new here.

So, I need to ask for some advice. There's a woman I've been seeing for almost a year. At this stage we are friends. Without going into details about her life - she's got a history, a very painful history from growing up that makes her very hard to trust people in general, and so any guy she possibly has a relationship with will have to be her friend for a good chunk of time - it's a trust thing with her. She's not a big fan of physical contact stemming from this as well. Now, I've got strong feelings for her, and I'm not a pushy sort. I'm not going to ever pressure her into a relationship or into intimacy and stuff.

My problem is, knowing when to initiate any sort of physical contact.

She's going through a rough time right now, effectively managing her household while her mom is sick, and she's stressed and down. Last night we went to dinner, and I could tell. She dressed nice for the occasion, gave me a gift (she made home made salsa,) and we enjoyed our time at the restaurant. But I re-iterate, she was down. I'm kicking myself because I wondered if maybe this would have been a good time to show physical affection - to comfort her. An arm around her shoulders, that sort of thing.

Is there a way to... "know" the right time, or is this something I'd have to guess at? I want to be there for her in anyway possible, but I don't want to overstep either.