Hi and welcome.
When you say you treated her for mange, was this on the advice of a vet? Has there been a follow up to verify whether it has fully cleared? Mange is usually pretty obvious in hair loss though, and thickening, reddened skin, not just scratching. It can at times be very difficult to get rid of. Worms are not that likely to causde scratching like this but earmites, flea dermatitis, allergies etc might, and all must be diagnosed by a vet.
You do need to see a vet as a first priority -- as noted, there are many medical issues that can cause scratching and your vet needs to eliminate those. Scratching due to food allergies is not that common but should be checked for as well as part of a careful elimination process. If nothing else helps than you should discuss SM with your vet and make sure they are aware of the problem in the breed. You can download info for your vet at
www.smcavalier.com.
Be careful if she is eating what you are eating (I assume that means table scraps?) as a lot of table scraps are high in fat and some human foods are not just risky but even deadly to dogs -- eg beware of onions, raisins, grapes, turkey skin amongst others.
I am afraid Bakers and the ovals are actually very mediocre quality foods -- pretty much anything that can be bought in the supermarket is lowish quality (which is what keeps prices low for small bags; but a good quality food bought in the largest bag will work out about the same. Good quality meaning Royal Canin, James Wellbeloved, Burns, Arden Grange etc -- there are many great options
) . If you read the side of the bag you will notice little to no actual meat content -- instead it will read 'meat derivatives', 'poultry meal', etc and lots of filler ingredients. If you do a search there are loads of threads on long food discussions (it is a favourite debate!! :lol
and they may be helpful. Bakers nd the ovals also have colouring and preservatives and grains that all can cause itchiness in susceptible dogs.
But as food is so unlikely to be causing the basic problem, and as a vet can help decide if this might be a food allergy, you should start with a visit to the vet and go from there.