I’m gonna say Clarissa given what you have maxed currently. Ursena takes a while to fire unless you have a lv 23 mana troop, and she doesn’t exactly have the tankiest build, so Clarissa’s elemental link really helps to keep your purple stack alive.
As much as I enjoy using Alfrike on offense, because of how slow she is, I almost wanna say you need to pair her with Clarissa to protect her against specials and buy more time for her to fire.
Freya is a bit more niche and doesn’t really synergize too well with what you already have. Of all the choices you listed, my vote goes to Clarissa since she will have the best synergy with your current heroes, and will become even more useful as you ascend more purple 5* and start running 4-1 or even mono.