When I started my 2 on raw I knew they were slim and abut the right weight so I started them on 2.5% of their weight as most people suggest between 2% and 3%. So for Tilly, assuming 11.5 kg is the weight you want her to be, that would be about 290g per day. After a while I decreased William's slightly and increased Louis' slightly. Now almost 5 years later, they both have about 2.2%. So don't worry if you don't get the % right straightaway as it's easy enough to feed a bit more or less if Tilly loses a bit of weight or puts some on.
I started by feeding 1 raw meal per day and 1 kibble, because I was feeling cautious. If I were to change a dog now I'd just go straight to raw. Most raw feeders don't recommend feeding 1 meal of each. Kibble takes a lot longer to digest than raw so the reason given for not feeding both is that undigested kibble may slow down the digestion of raw. However, when I first fed raw, from 1987 until about 2002, I fed raw meat and a biscuit mixer together, because that's what most people did then. My 2 Cockers thrived, although it probably did have a bit of an effect on their pooping as it varied in consistency on a daily basis much more than with my current 2 raw fed boys (apologies to anyone eating their tea)
I know that some people on COL (Helen for one) feed 1 meal of kibble and 1 of raw successfully, so if you want to make a gradual swap by doing it that way then go for it. Feed 1/2 her current daily ration of kibble for 1 meal and 1/2 her daily ration of raw for the other.
I've looked at the link you posted and it looks like a good "complete" raw and I see they do some without added veg. too. You might want to ask roughly how much bone is in the minces as anything more than 10% may be difficult for Tilly to cope with at first and may give her constipation. It did with William but Louis was fine.
Nowadays I feed about 50% "complete" minces and about 50% DIY raw (chicken wings and backs, whole lamb hearts, duck necks, chunks of chicken, turkey, green tripe or lamb and some lamb liver and kidney added a couple of times a week). That gives them more variety in taste and texture, cuts the cost a bit and enables me to customise their diets a bit to suit their individual requirements. William doesn't cope with as much bone as Louis, so sometimes Louis might have a couple of chicken wings or a carcass for a meal while William will have 1 chicken wing and some green tripe or other bone free meat.
You might want to stick to 1 protein source for the first week, chicken is usually the one suggested, and then start introducing others. Ultimately, a variety of protein sources will give the most balanced diet. Oily fish is very good too. Mine have fresh sprats once a week when in season, or any other oily fish I can source. But be warned, the first couple of times they had sprats they threw up afterwards. I think I gave them too much in one go instead of introducing it gradually.
Hope it goes OK
