I just did her quests and all she gave me was Shinwas Coal 
I am new so I don't know if she hands out valuable stuff, so I'm asking for your experience, do you think it's worth it to do her quests?
She does hand out valuable stuff, but it's a gamble, you can get junk from her 3 or 4 days in a row
Yes the majority of her items, tend to be stat boosting items that you can either resell for a nice profit or use on a battle pet, Most of the boosters tend to go from hundreds of thousands of sP to millions of sP. Keep at it with her quests and they will pay off in the long run.
Even if she gives you a booby prize for the day, you're still doing quests you probably would eventually do otherwise so to be honest I don't really see a negative side in doing her quests daily.

Thanks :) It's still so hard to discover things! I just discovered there is another quest giver called Major Drills.
I wish there was some kind of homepage where I could click the dailies like kissmoto was on neopets. :( It's hard to explore through the map and click things to discover what they are.
Yeah Subeta has a lot of things that are scattered about, you can try this page for dailies. Though of course not everything is on there, like Ruffie Raffle is on the games page for some reason.
But you can put a list of all quests on your sidebar by going to the edit sidebar page here and clicking the (add) link next to Quests, and it lets you know how many quests you've still got to do for that day, very useful.
Thank you so much! That's the first time I'm seeing that page, I didn't know subeta had an official dailies page that is so cool! I added the link to my bookmarks now <3 should make it a lot less confusing for me~