thumb sucking

Good morning, My daughter is turning three in 2 months. She sucks her thumb for comfort pretty regularly. In prior visits, her pediatrician has told us most children stop around 2-3 years old on their own. It doesn't seem to me there are any signs of her just giving it up. I actually have an ultrasound picture of her very clearly sucking her thumb in the womb. She had a very thorough exam with her dentist & her top pallet is being affected by pushing her front teeth out. So, we have decided it's time to help her stop. I hear it progressively gets more challenging as the child ages. I bought her a tgaurd for her right thumb since it had the best reviews & offers a refund for 60 days. That website suggested that young children might switch what finger/hand they suck so we got bitter stuff for her other fingers. We have mentioned it to her a few times, but it does not seem like she remotely understands. Are we on the right track on guiding her through this ASAP? How do we effectively pre-teach this process with her & what suggestions do you have to help us in this endeavor? Thank you for your insight!