I'm glad that things are going well. :3 Hopefully she'll reach end-game soon, and can begin truly playing with her crafters and gatherers. :3
Don't let her get too discouraged or burnt out during the 2.x MSQs. There are a bunch of them (over 100 MSQs before you reach Heavensward content), but it will probably take her less time if she isn't particularly interested in reading/watching cutscenes, or doing all the level 50 dungeons that you have to do via Sidequests.
I really have to disagree with this post, and I am not aware of this, in any way, being an accepted status quo of this game, nor would I recommend it for any player.
Supplementing experience with PotD is fine; the MSQ does have several lulls where you need additional levels before you can unlock the next quest, and using PotD, if you don't feel like running dungeons, is fine for doing that. Same for leveling alternative classes to level 15 or for relative cross-class skills (THM to 26 is just painful most of the time).
However, running PotD until you're level 60, and then deciding to do the majority of the MSQ and your job quests? That is a lot of wasted MSQ experience, which only gets buffed more and more as the game expands. I do not recommend throwing that away.
PotD, with regards to some classes/jobs, is extremely different compared to actual dungeons. I think, in a way, it can apply to all jobs, but mostly this applies to tanks and healers. Incoming and outgoing damage in PotD compared to dungeons varies significantly, and leveling a tank in PotD especially, I feel, doesn't prepare you for content once you reach max level. Same thing for healers. With the current speed-run mentality surrounding PotD, I also do not feel like it provides a good learning environment for those who are not the quickest of learners. Leveling up the old-fashioned way, and getting your skills in a more paced manner, I feel allows you to learn how to better use them, if you choose not to supplement with reading guides and tips online.
Also, PotD monsters do not have positionals, so DPS jobs with positional requirements (MNK, HW DRG, NIN) do not learn the importance of how positionals can affect your damage. And a lot of mechanics present in dungeons or 8-mans or 24-mans, are not really present in PotD, and if they are, only very briefly during the boss fights, which are usually just cheesed to high heaven anyways.
Aside from getting a Padjali/Kinna weapon, you will also be sacrificing gear, which is needed for progression. If a player doesn't have the means to get crafted gear (friends, gil, etc.), then dungeon gear is the easiest way to gear up. I have met a lot of "PotD levelers" with gear so bad and so under-leveled that it makes some dungeon runs unbearable. And I know that they have to be PotD levelers, because they sport their Padjali/Kinna weapons in a dungeon like The Aery or The Vault, while still wearing a mixture of i90 or Unaugmented Poetics gear. When you're having to heal a tank like this, it is NOT fun.
Perhaps I am just old-fashioned, but I would not recommend to any new or serious player to use PotD as their sole way of leveling.