4-5 days and she will have started losing condition. Check her breast and feel for the 'keel' bone. She should feel meaty with some or little bone protruding - as I've said before, check a healthy bird for a good comparison, but orpington should be in the 'meatier' side with less bone than most other breeds. If the breast is thin and the bone very prominent, then she is wasting away.
Tube feeding, if you have the right equipment, can be relatively straightforward, but you did mention her crop is not empty?
An empty crop should be able to hold 60-80ml of food. - too full and they run the risk of regurgitation and asphyxiation. When tube feeding, I aim to give around 50ml and use thicker or thinner solutions depending on their condition. Also, a rather long tube (oiled with olive oil), which can reach most of the way down the throat, but not so far as to enter the crop - you really just want to get past the windpipe (which is the hole at the base if the tongue).
With her condition now, and if her crop is not completely empty, I'd stick to very soft watery foods in small amounts. Avian probiotics and vitamins like Polyaid, electrolytes, and apple sauce or lorikeet wet mix would be a good starter slurry. The waterier it is, the thinner tube you can use, and the less obtrusive it is. Maybe start off light, like 25ml 3x a day and keep an eye on her crop speed (or how quickly it is emptying). If it isn't emptying, try massaging the crop to coax it down, but hold off on feeding more until it has emptied.
She may be on her last leg here and digestive system already shutting down if her crop isn't moving.
With soaks and things like crop massages, the longer the better - 10 minutes is quite quick for a therapeutic soak. A person would probably soak for at least 30 mins before they started to properly relax. I'd hold off on any baths (unless cleaning the rump) if her body condition is poor, which it likely is, as frail birds don't fare well with heavy handling.
*I should mention the crop should be emptied by the next feed time, if not, then massage. It shouldn't be expected to empty immediately after a feed. Oh, and any slurry you give her should be warm, but not scalding - like it should not burn the inside of your wrist. Never tube feed a sick bird cold food.