Spider. Post screenshot of roster.

Athel - try getting her to level 60 as soon as possible. Of course you should put artifacts on all champions that you use - but not upgraded to level 16, just to 8 or maybe 12 for the better pieces. 

The really rare resource, which you should be very careful about spending, is skill books. Especially epic and legendary ones. Artifacts are easily replaced or moved between characters at the cost of some silver, skill books are not. 

It would't hurt to advise your full roster as Trips said, or are those the only rare / epic heroes that you have so far? 

Putting some rare skill books into Athel is fine I'd say, she could remain useful for quite some time and rare books aren't too hard to obtain later on. But she does require quite a lot of books to fully develop, not sure she's worth all of those. In many cases, a hero may have one or two skills that are worth putting books into while the other skill(s) are not worth it - but sadly it's random, you can't choose which skill to level up. Mostly reducing cooldowns or increasing buff/debuff chances on skills will be more important than damage bonuses. 

I mean, I also fully booked my starter hero, Shaman and some others who weren't fully worth it in hindsight. It's not like that ruins the game forever or anything - but when you get to the point where you have a dozen or so heroes that you'd like to develop and you only occasionally obtain new skill books, you start to regret all the ones you wasted early on on heroes that aren't remotely as good. 

I second focusing on Athel based on what you have mentioned you have.

Dont worry too much about the rare books. Id suggest maxing out her skills, she is not in the top 5 rares but but she can do well in most aspects of the game and unless you pull a better rare really soon you will start to get new books.

Better rares are kael, apothecary for sure. Later on coldheart and bellower will become better.

I highly suggest equipping her with a vampire set for sustain early on.

Screenshot: https://ibb.co/mBrXDXT

Inteleria has a page with Champion ratings including each area as well as overall Tier. This should give you a good start to figure out which Champions to focus on. https://www.inteleria.com/champion-ratings/