Does one who experiences an involuntary surge of desire within her, which then subsides as it does after marital intercourse, although she does not derive pleasure from it and it lasts for only a few minutes, have to perform ghusl?

If the feeling is merely a whisper (waswasa), then one should disregard it. If a woman feels genuine desire and a fluid is discharged:

If it is maniyy (spermatic fluid), which is thin, yellowish, and its discharge is accompanied by pleasure, then ghusl (ritual bath) is obligatory.

If it is madhiy (pre-seminal fluid), which is discharged when desire is aroused but without pleasure, then wudu' (ablution) is obligatory, and one must cleanse whatever it touched.

If a woman is uncertain about the type of fluid, she may choose between the two and adopt the ruling for one of them. If nothing is discharged, then nothing is required of her.