Does prayer become invalidated by obsessive doubts about the intention, and what is the ruling on interrupting prayer due to obsessive doubts, and is it obligatory to repeat it?

The most effective treatment for waswasah (whispers/obsessive thoughts) is to ignore it. What the questioner feels, a desire to invalidate the prayer, is a result of waswasah. Therefore, she should not pay attention to such a feeling, but rather seek refuge in Allah, complete her prayer, and not repeat it. Indeed, whoever is afflicted with frequent waswasah should distract themselves from it. The original intention of the prayer remains valid and is not nullified merely by hesitation about discontinuing it.