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If she is acting normally apart from coughing and producing only a small amount of blood, you may be able to keep her as quiet as possible and wait. If she is coughing up a lot of blood or starts to act abnormally, she is likely to need veterinary care.
If the blood is coming from her mouth, she may have bitten her tongue or cheek or bumped her gums. She may have bruised her lungs causing some bleeding. Often blood from the lungs will come out the nose and/or mouth. Blood from the lungs is often (not always) foamy.
If the blood is coming out her nose, sensitive structures in her nose may be bleeding.
Apart from keeping her quiet and letting her drink, there is not much you can do at home. It sounds like you fed her, which is fine. She does not need to be fed extra and limiting her food for 12 hours would be reasonable.
Let me know if you have follow up questions.