So should I not grab her as a healer then? Who would be better? Sorry for all the questions, guys.
You don't get a choice.
When you do the event, she'll open up for you, and even the worst healer in the game that has 4star white healing (that's not her by the way) is 10x better than White Mage. The cores are terrible. Tyro an exception, but on how he's good is another story.
As for pulling on banner for Ysh, just read MCA and Balphon counter arguments and decide for yourself. I don't have either of the good stuff for Ysh, but I have a TON of healing BSBs and medicas (in this game, any group heal is a medica).
Mythril is somewhat rare, but since you have story dungeons, you truly control your mythril count. It will take you several months to get bazillion mythril offered in Story dungeons.
Edit: Now if you were spending gems, aka, real life money then it really becomes a debate to scrutinize. You (sorta ought to be) far away from wanting to spend RL money, since mythril is at your disposal. But if you truly get hooked, you may find yourself going that route. This game broke me of "mobile games are half-ass experiences like Angry Birds" and "who the hell is stupid enough to pay real life money for gambling on a video game" thoughts that I had coming over from ps4 and a gaming computer.
Edit2: By the way, have you ever heard Shaq call in to the radio show Lex and Terry? That show is big in TX and Florida. Whenever Shaq would call in, I couldn't stop laughing, dude is funny as hell.