Tough answer as there are many girls with horns and many with armor. However not with both. But are you talking about horns as in horns that are physically mounted to their heads? or ones that are attached to a helmet of some sort? But whatever the case, here are a few I thought of.
Aqua (armored form) - Kingdom Hearts: BBS
Arrancer girls (many types of them) - Bleach
Shania (fusion form) - Shadow Hearts: New World
Laura Bodewig (armor form) - Infinite Stratos
Erza Scarlet (giant or purgatory armor) - Fairy Tail
Hope this helps as these are what I think fits your criteria best.
When in doubt, just take the next small step.
With that next step take a deep breath. It calms the mind.
When the mind is calm you realize the best is still yet to come.