Everything below is at x1.00 damage unless otherwise specified.
Sekhmet armour takes 75% damage.
Each hit of Beam is 425 * 0.75 = 318.75 damage per hit on sekhmet (the game rounds up in this case for some reason).
It's 59 hits in the super.
59 * 319 = 18,821 at x1.00 damage.
That means it will always kill sekh, point or assist, unless you're solo Eliza vs non-solo robo.
Fortune's head is not in play as an assist unless the assist is specifically a head move, so assist fortune doesn't actually take more damage unless she has that assist.
If head assist fortune is hit with level 5 beam super, both will be picked up and it will leave fortune with a whopping 173 health with the super dealing 15,327.
Level 5 beam super will do 12,726 damage (according to training mode), so 12,726 * 1.3 = 16,543.8 (estimate because scaling will change it slightly) which is enough to kill as a duo vs a trio, but not enough to kill trio vs trio. However as as solo, Level 5 beam does 12,726 * 1.45 = 18,452.7 damage which is enough to kill fortune any time if the head is picked up with her.
To sum up, Level 5 beam does:
18,821 damage at x1 vs sekhmet = death to sekh unless solo eliza vs non-solo robo
12,726 damage at x1 vs Fortune + Head = Death to fortune if Robo has a ratio advantage
15,327 damage at x1 vs Assist Fortune + head = 173 health left on assist fortune, or dead if robo has a ratio advantage or both are trios
7,383 damage normally on any individual character.
10,271 damage normally on any individual assist.