Novenas, or other repeated prayers such as the Rosary (where you repeat the decade 5 times, the Hail Mary 10 times a decade etc) aren’t superstitious as long as you are praying with the understanding that “God’s will be done”, not that if you say a prayer X number of times God will magically grant your wish.
It doesn’t matter if you say the prayer once a day for 9 days, or 9 times in a row right this minute with a 10th one for thanksgiving. God is outside time. Mother Teresa could have prayed the prayer just once and there were certainly many other occasions when she said just one prayer. I’m sure she said it 9 times with an extra one for thanksgiving because it was a way of quickly praying fervently in an already-established form (that of a novena), not because she thought 9 or 10 prayers were a magic number.
Likewise, there is nothing wrong with “thanking God ahead of time” when you pray. There are other novenas that do this (the Church-approved 54-day Rosary Novena has 27 rosaries of petition followed by 27 rosaries in thanksgiving) and other saints and blesseds who advocated doing it. The idea is that you put your needs in God’s hands, trust him to provide what you need, and thank him for being a loving God and providing for you. Same would apply to thanking Mary, St Joseph or any saint for hearing our prayer and interceding for us.
Mother Teresa had great trust in God and in Mother Mary and would have accepted any result that was provided, even accepted it if God chose not to answer her fervent prayer. Nothing superstitious about her, or the prayer.
Repetitive prayers don’t have to be meditative, by the way . The Divine Mercy Chaplet, given us by Jesus himself, is repetitive, but not meant for meditation. St. Faustina would be saying it all day while going about her work at the convent; she clearly wasn’t sitting down and reflecting and meditating. And that’s fine to do. Maybe you wouldn’t want to use a Rosary or the St. Bridget Prayers for that purpose as they’re supposed to be more meditative, but it would be okay to just repeat a bunch of Hail Marys or Memorares as well, as long as you weren’t thinking in terms of hitting a magic number that would get God’s attention, because you have his attention.
