has gone from 75th to 25th centile in weight, although thankfully she has not lost weight.
Did you mean here that her height/length centile had dropped but weight is steady? Height/length might level out with the next growth spurt.
My DS also took very little milk (around half the advised amount, always worrying for me!) but weight was steady so although I worried terribly he did gain well.
I always gave milk an hour before solids and in the early days he would want milk straight after solids too which actually increased his intake so it's worth a try to get some more milk in. I agree that it is very difficult to make them take milk if they just won't take it, but I'd still keep the focus on milk as much as you can, as Sara said this is their primary food, it contains more fat and nutrients than solids at this point.
You could also try adding milk (formula or breast) to home made purees rather than water and perhaps some solid foods made with milk such as milk pudding (just thicken formula with corn flour and heat until thickens, add flavours which are natural such as whizzed soft berries or a smooth apple sauce).
Do the jars you use contain sugar? Some of them are very sweet which could be one reason for her preferring the jars. You might try adding some sweet fruit to your home made purees to see if they are more palatable for her, a small amount of raisins added when you puree will spread sweetness throughout the food. I would continue with the finger foods too, sounds like she likes those even if not so much gets eaten. To reduce the 'burden' of cooking lots of puree which is rejected you might be able to just whizz a small amount of the food you make for the family/adults and also some of the veggies as finger food.
I would also offer cheese to increase her dairy/fats intake. Fingers of cheese to gnaw and suck on, cheese sauce or grated cheese, or some added to the purees (which also kind of seasons food, I added cheese where I might have wanted to add salt for instance).
Not sure where you live but in the UK all babies are recommended to take a daily vitamin supplement (in drop form for this age) you might want to look into that too, formula has all the vits and minerals needed but if she isn't taking much then she's missing out on these.