What is the ruling regarding someone who suffers from severe obsessive-compulsive disorder (OCD) concerning ritual purity (tahara) and ritual bathing (ghusl), causing her to repeat ablution (wudu') and prayers numerous times, and to fear that any discharge she sees is semen, leading her to constant anxiety and fear?

The best cure for waswas (obsessive whisperings/thoughts) is to ignore them. Ghusl (ritual bath) is only obligatory for discharges if it is mani (seminal fluid). For women, mani is thin and yellowish, and may be white. Its smell resembles pollen or dough, and when dry, it smells like egg. If you doubt whether the discharge after a wet dream is mani or madhi (pre-seminal fluid), ghusl becomes obligatory. However, if the doubt wavers between three possibilities, then ghusl is not required of you.