Where's Gunnthra (My Trials to Summon Her)?

Short Story: Does anyone know when's the next time we can either summon for Gunnthra or possibly see her down the road for free because I cannot find it in the banner description?

Long Story: I've wanted Gunnthra for a while, but it's been a struggle. I want at least one of every legendary hero element and I want to pair her up with my +Res Sigurd. I did not summon on her debut banner because it was in between Winter's Envoy and Happy New Year. Last month I vented about using probably 200 orbs to Summon Legendary Ike for free, 2 PA Azura's (when I already have 1)' and 3 Summer Xander's I did not want. This month, I've probably spent over 150 orbs to Summon a neutral Shiro, neutral Dorcas, and a second Summer Corrin I did not want (even though this one is +Spd/-Def). I am more accepting of this month's results compared to last month, but I am getting tired of summoning on these banners for the Legendary Heroes. I'm fine attempting to get Ephraim next month, but the journey to acquire Gunnthra does not want to end with me.