1. Laali could not have poisoned her because she is not allow to go out of her room, leave alone the house and into the market. The poison med bottle was brought from outside. Laali doesn't even have money to buy anything.
2. Gangiya was taking Laali to the Thakurain's room at the wrong time, and AFTER the room was left unattended. So, someone who does have access to the outside world, could have gone in, substituted the bottle and slipped out.
Loha saw G take Laali out. He knows Laali is in her room almost all the time. It couldn't have been Laali who poisoned Badi T.
3. But Siddy did come in to leave a towel and looked shifty, which Shekhar saw. Nadini could chime in that she didn't even eat her food, she was gone from her room...where was Sid? Switching bottles.
This could convince Loha that Laali is innocent.