Sne is summoning unless you have manga proof to say she won't?
She can easily reconnect her arm like madara did to zetsu arm.
im not going to explain this again but i will try.
jumping to the ritual part.
sakura walks
hidan stabs his leg
sakura drops, her leg heals she gets back up
he stabs her in the leg again
no mater how you put it sakura will not walk no matter how much her leg regens that is my point. hidan will figure out she is regenning and will keep stabbing her sakura isnt moving anywhere.
and the summoning the proof is that she has
NEVER summoned the slug for combat. not in her fight with sasori, not with madara, not with juubi clowns. she has only summoned the slug for support and healing. based on that she has no reason to summon it now and as i said if the slug did spray the field with acid that would seperate hidan and sakura. hidan across the field would freely use his ritual
you also have to take into account that she would let him use the ritual because she is analytic. after he starts making the symbol she will watch to see what he is doing and then she will lose.