What is the reason for and solution to my daughter's problem of avoiding prayer due to repeated invalidation of her ablution during ablution or prayer, even though she does not suffer from any health issues?

What your daughter mentions about her ablution being invalidated might be waswasa (whispers from Satan), and you should teach her that the default is the validity of her purity, and that it is not invalidated merely by doubt. The reason might also be psychological, so it is advisable to consult a trusted doctor. You should make her love prayer and mention its virtues, and that it is a connection between the servant and their Lord, and that it is the most beloved of deeds to Allah, while being gentle with her and making her feel the ease of prayer. You can benefit from the book "Prayer, Why?" by Sheikh Muhammad Ismail Al-Muqaddim.