Barbara, indeed, is a good healer in the game, especially when you are starting out and don't have any other healer besides Noelle. Noelle is a good healer, but when it comes to elemental reactions, Geo serves a neutral purpose. Barbara can help you in teams that need reactions like Freeze, Vaporize, Bloom, etc. You can use her elemental skill to heal your active character, whereas Noelle has to be on the field to heal the team. Noelle's heals depend on the RNG, and Barbara has consistent heals. I'd say that you should equally invest in both characters and use them accordingly.