I partially agree. The build order probably needs to be changed. About the mana items though, I feel that Frozen Heart and Rod of Ages are real good items to use on Karma, seeing only her E has decent range. If you want to for instance just not use Q for damage but just for healing, then sure you could change those items up, maybe swap the Archangel's Staff around for a Deathfire Grasp although I feel that with the amount of mana you have gotten from Frozen Heart and Rod of Ages Archangel's Staff is a decent choice.

If you got any suggestions, please let me know!

I like the idea, but I don't like the build order. Double gp10 then Catalyst then Tear? This not only means you have almost no AP mid game, I also doubt Karma needs that much mana, since she's constrained by Mantra stacks.