Is it obligatory to perform ghusl for every prayer when vaginal discharge occurs upon merely thinking about one's husband or speaking with him, even if it is a normal conversation?

The fluid that exits a woman's vagina due to arousal is of two types:

1. Madhi (pre-seminal fluid): A thin, sticky, whitish fluid that exits upon arousal. It is not followed by a weakening of arousal, and its exit may not be felt. It is impure (najis), necessitates washing whatever it contaminates on clothing or body, and only nullifies ablution (wudu') without requiring a full ritual bath (ghusl).

2. Mani (seminal fluid): A yellowish, thin fluid whose expulsion is pleasurable for the woman, and she feels a weakening of arousal afterward. Its exit necessitates a full ritual bath (ghusl), and it is pure (tahir) according to the most preponderant opinion.

What the questioner most often experiences is madhi, for which ablution (wudu') and washing whatever it contaminates on clothing or body suffice. There is no need for worry, as it is a natural occurrence. It has been authentically reported that Ali (may Allah be pleased with him) used to experience frequent madhi, whereupon the Prophet (peace be upon him) instructed him to perform ablution and wash his private parts.