Personally, I would not give a lot of extra vitamins, if feeding a nutritionally balanced poultry feed.
I wouldn't do anything about a fat pad at the keel bone on an older hen that is sitting around a lot. Not sure why you want to reduce it, I would leave it alone.
Skin can get a bit dry on chickens just like anything else. I don't really see anything that concerning about her face or skin, but if you are worried about it, a VERY light coating of vaseline can be applied to the facial tissue, combs/wattles. I am talking about put a very small dab of vaseline on the fingers, let it become melty, then apply lightly to the skin.
I can't say why she's panting more - may be the warmer weather, could be difficulty breathing, hens with reproductive disorder often have distressed breathing, could be pain/discomfort... If it's not that hot now and fans are not helping, then it sounds like she's going to have a harder as temperatures rise.