The second Candle walks in, she lets you know that she has to go to the bathroom because her bladder and bowels are full. This is exactly what you wanted to hear because you love humiliating her and making her beg for things!
If she really has to go, she won’t mind doing a couple of tasks to prove that she really has to go, right? Getting tied to a chair (off camera) should be an easy thing to bear if she really wants to go so badly. It is not your problem that the ropes dig into her growing belly and makes her more uncomfortable. It also is not your problem that she does not like having her hand put in a bucket of water which makes it harder to hold her swelling bladder.
It would make it even more amusing of a challenge if she would do a little dance while she is proving her mettle. Of course that would still mean that she needs to go back into the bondage chair after her performance, because she still needs to put on a good show. The best thing for someone in her position is a little tickling. Yes, that is the ticket.
At this point, she is completely desperate and willing to do anything. She offers to pee herself in front of you if she can just get out of the bondage chair and stretch her legs and let her bladder completely decompress from the pressure that has been building up.
She is so embarrassed as she loses control and the pee floods down her legs.