How lovely of you to look after these feral cats! I would be concerned that Daisy may have dental problems preventing her from eating dry food. Those can be very painful. The only thing you can do for her is take her into a vet asap. The vet can examine her mouth and can discuss treatment options with you. If she does have a dental problem, she will need a dental cleaning, scaling, and polishing to fix it. I can give you some resources that may help you afford a vet. You can see if your vet accepts payment plans, if there is a low cost clinic in your area, or you can apply for Care Credit online. There is also an organization called Red Rover that give grants for treatment of sick animals, and you can see if you qualify for one of their grants. Best Friends also has a list of resources that offer financial assistance on their website.
http://www.humanesociety.org/animals/resources/tips/trouble_affording_pet.html?credit=web_id91754962https://www.redrover.orghttps://www.carecredit.comhttp://bestfriends.org/resources/financial-aid-petshttp://lessonsfromaparalyzeddog.com/when-pet-owners-cant-afford-veterinary-bills/The Feline Veterinary Emergency Assistance Program is a nonprofit 501 (c)(3) organization that provides financial assistance to cat and kitten guardians who are unable to afford veterinary services to save their companions when life-threatening illness or injury strikes.
God's Creatures Ministry helps pay for veterinarian bills for those who need help.
The Onyx & Breezy Foundation has many programs including helping people with medical bills. They are a good resource for information.
Brown Dog Foundation provides funding to families with a sick pet that would likely respond to treatment, but due to circumstances, there is not enough money immediately available to pay.
IMOM is dedicated to insure that no companion animal has to be euthanized simply because their caretaker is financially challenged.
I hope one of these resources helps you!