Is the arousal a girl feels weeks after she has stopped masturbating, which can occur at any time, considered a natural discharge that prepares for intercourse, or could it lead to the forbidden?

The evil thoughts and imaginations that come to the heart are not held against a Muslim. Resisting them and not dwelling on them is the correct approach. Satan is an enemy of humankind and might intend, through such thoughts, to lead you to sin or distract you from what is beneficial. Seek refuge in Allah from his evil, avoid everything that arouses lust, such as forbidden glances, beware of the company of bad girls, and keep company with the good. Stay away from sins in general, for Satan might be given power over a person because of them. Masturbation is forbidden and harmful, and one must stay away from it and repent from it. Marriage is among the best means to achieve chastity, and fasting is also a means to overcome lust.