G.T.
I'd say 5 or 10 minutes per session if you can get her to willingly sit for it. Make sure you take a picture for the photo album. I was just looking thru some old albums the other day and I have a whole section devoted to fat lips, black eyes, scrapes and bruises... it's funny to look at it now, but I sure hated it when it happened.
If she seems fine I wouldnt worry too much about icing it, it's not like a mandatory thing to do, so if she doesnt let you it's not anything to get overly concerned about. I'd use frozen peas and wrap the bag in a thin dish towel. The main thing you dont want to do is cause freezer burn to the skin, so just be logical about how long you hold it on there.