In the light of my other topic Traits, talents and their usefulness and how your game works I say that Astral Mother is just mediocre.
It looks like somebody hates centaurs since not one troop is useful which is centaur and Astral Mother is no exception.
The dmg is weaker than beetrix’s. It needs at least 14 gems to reach beetrix’s dmg, costs more and she is a mythic. It can be higher but having more than 14 gems of the same color on the board is rare even when there is a storm. After any gem create/convert the naturally matching gems decrease the number. It takes a very bad convert to have many gems of the same color. But it after all it’s not that bad.
She does not take off the gems with full effect. It could increase her usefulness greatly, The Gray King is considered a top tier mythic and has a similar spell effect and much better traits.
And here we are at the third trait. Really 40% chance on turn to give reflect to an ally when Mirror Queen has 100% on 4-5 matches! That trait is just lame on a mythic.
So here are my suggestions.
Dmg is okay, make her spell to remove gems with full effect, replace the trait with Mirror Queen’s or if the turned base trait remains make it to give reflect to all ally with 100% chance. With these improvements she would be a decent mythic and would give us a nice centaur troop.