Well I detailed my thoughts in a VM to her. The TLDR of it is that she's pretty much the only one that can take Jangmo-o down. Robin is too far away and Mr.Mime(F) is in prime position to go after Waterproof(who's vulnerable) or you. I believe she's too far away to give Unicorn any real problems and Alex is immune to her Psychic attacks. Pretty sure it lacks a Fairy move or Alex would be in for a real shock. Therefore, I'm the one that has to go and lock Mr.Mime down with Fire Spin. Doing so would prevent her from going after anyone else in the party while setting her up to be attacked the following round by Mercy's Shadow Sneak(Ghost > Psychic).
How Lily attacks Jangmo-o really doesn't matter. If she uses her last use of Ice Cream, its a KO if it hits. If she uses Absorb, she has a 60 SpA stat + Miracle Seed to boost it further. Jangmo-o only has 10 HP so she might do enough on Absorb to finish it off despite it being NVE(x1/2). She'd also recover a bit of HP in using Absorb that is boosted by Big Root.
If I were in your shoes, I'd post my move as follows: I'll move to F13 if and only if Jangmo-o still stands and use Vine Whip against it to finish it off(or try to anyway. If its still standing, it'll faint to Poison but get off one last attack). If Jangmo-o has fallen, I'd move down one square(I14?) and use my Fishing Rod on the item in the Lake(which if successful would pull it to L14). I thought about the move to G12 and using the Fishing Rod on Robin but Plan B would yield the following outcome:
Jangmo-o falls(by Ice Cream, or combination of Absorb and Vine Whip)
Snubbull-A falls(by Waterproof's Ember)
Houndour falls(by Unicorn's Force Palm in OHKO fashion)
Snubbull-B falls(by Mercy, Susato and Robin ganging up on it). A thought did occur to me on Plan B that if Robin and Mercy do enough damage to faint Snubbull-B, Susato might be in range to grab the item at L14.
Mr.Mime is locked down(by me)
Nidorino is wounded and possibly flinched(by Alex).
Of the two plans, I'd lean towards Plan B with the option of fishing the item out of the water. Priority is Jangmo-o though.