Are there any supplications to restore sincerity in the heart and commitment to prayer, and what should I do if those supplications fade, especially with the questioner's feeling that she possesses the characteristics of hypocrites and lacks sincerity?

Sincerity (ikhlas) is the basis for the acceptance of deeds, and Allah accepts nothing but what is purely for Him. Among the means of achieving sincerity are: contemplating the greatness of Allah, striving against one's self (mujahadat al-nafs) for it, knowing the danger of showing off (riya'), and seeking help through supplication (du'a).

As for negligence in prayer, it is a grave sin and indicates the characteristics of hypocrites. Prayer is the first thing a servant will be held accountable for on the Day of Judgment, and abandoning it is disbelief (kufr). Remorse over shortcomings is a sign of goodness, so one must continue to perform good deeds.