What is the ruling on my sister repeatedly redoing her fast due to her obsessive doubt about gum blood or saliva reaching her stomach?

If blood emerges from inside the mouth and is swallowed intentionally, despite the possibility of avoiding it, the fast is broken and its make-up becomes obligatory. However, if the blood overwhelms her and reaches her stomach against her will, her fast is not broken, by analogy with one who is overcome by vomit. The mouth is considered to be like the exterior, so if a fasting person swallows blood or vomit that reaches them, their fast is broken, unless saliva is excused due to the difficulty of avoiding it. As for mere doubt about blood reaching the throat, it has no effect.