Hi Toffeegigsy and welcome to the forum! I'm really sorry to hear of your poor girl's troubles. The priority should certainly be to settle her stomach as without that foundation, any new food is likely to just make things worse.
Although I am no fan of Royal Canin, their GI diet can be very effective at easing digestive problems and may be worth considering, at least until the worst of the problems have subsided. Another alternative would be the good old tried and tested rice and chicken approach:
Day 1: no food at all
Day 2: a very small amount (no more than a few spoons a couple of times a day) of very well cooked brown rice. It really does need to be cooked far more than you would do for yourself, until it is overcooked and stodgy. You can cook a large batch at the start of the process and take from that rather than cooking every day.
Day 3: A bit more brown rice and add in a little boiled chicken.
Day 4 onwards: a bit more brown rice and chicken.
Whether you go with Royal Canin, chicken & rice or some other option, the whole point is to rest the system and allow any damage that has built up over the course of the problems to heal so keeping the feeding amounts low is key.
The solid motions are what you're aiming for as they are a sure fire indication that the system is back on top of things. Now that she's solid, ideally for 2-3 days, you can start to phase in whatever diet you would like your dog to be on long term. Whether that is a commercial dry, wet or raw or a home prepared diet is up to you but whatever you choose, do ensure that the ingredients are high quality and highly digestible. We have a guide on picking the right food here
. If you suspect your dog is allergic or intolerant to any foods, definitely avoid them for now.
The new food should be introduced incredibly slowly, replacing a very small amount of the temporary diet with the new food. In the case of a dry food for example, this would be no more than a few biscuits for the first meal or two. Provided the motions remain firm, then increase the amount slightly on the next day and so on until, after around 10-14 days, she is 100% switched over to the new diet. If, at any stage, the digestion looks like it's struggling (i.e. if the motions start to loosen) then slow down. Go back to the last ratio of new food that didn't cause upsets until the motions once again firm up and then continue the switch at an even slower rate. If the problems keep coming back, then you will have to try another food.
This process can be very tedious and stressful but I have seen it work time and time again and it really is the surest way to reboot the digestive system and start from scratch on a new diet. Once she is properly recuperated, we can look at gradually getting her wait back up to normal.
I really hope that helps. Whatever you decide to do, please keep us posted as your feedback could help countless other dog owners in a similar situation.