Edit:

Originally Posted by Mindrunner

Still have it, except when I collect a present. Let's hope the next maintenance in about 2 days solves this.

Just got it again several times in a row, both collecting and raiding didn't solve this time. Running a mission fixed it, but it seems this is still going on.

Originally Posted by Maladaptive

Now, for some advice please. Thanks for any tips!

Well, what usually catches my eye in girls is usually team/map utility (Or Solar Blast potential but that's just me.)
So I'd probably go with:

SLICE:
Cherry Sage (2.5 damage, -10% attack for 3 enemies) (Debuff girls are very versatile)

HIT:
Edelweiss (event girl, 2x damage to 2 enemies), +10% heal squad from Pest Nest Nodes) (Healing on Pest + Speed buff to squad)
Adonis (event girl, 2.4 damage, +10% attack for 3 squad members) (Whirlwind/SpiderWeb disable is great)

PIERCE
Anthurium (2.4 damage, +22% attack for squad on turn 1) (Best girl in game. Fact. Also Speed buff utility.)

MAGIC:
Queen of the Night with two equip slots (x3 damage to 2 enemies, 2x squad healing) (Double Squad healing)

All of them have some type of ulterior utility they can bring, but I don't really know which of those might be actually important to you or not.
But you should definitely level up Anthurium.