I was firstly excited to see Evelyn’s crystal in the shops daily deal section but I then realised it was priced at 500 gems and not 300 gems as per all other followers crystals when they appear in the daily deal. Evelyn’s crystal is always in the store for 500 gems in the Bundles → Other section.
I suggest Evelyn’s crystal is repriced for 300 when it appears in the shops daily deals just like the other follower crystals.
I’ve wondered about this myself.
My guess is that Eveline’s crystal is more expensive because each individual crystal can be used for a specific benefit in her legendary/mythic relic conversions, while an individual crystal for any of the other followers has no specific benefit (only useful in specific quantities to ascend/level up the follower).
An official statement on the reasoning for the pricing difference would be nice to hear, though.
I do believe you’ve just given them one 
