As she feels more of the dildo she naturally puts her feet down as her body stiffness causing the rope to hit all the mechanisms causing the other to move up and down or just the dildo into her like a machine

Or also could have where to add she can partly pull herself up by feet thing making it worse for the other girl and as tired fall back in harder and left In so long no energy to properly ever hold herself up and just keeps trying instinctevly and makes an endless loop for both of them and also where the other can see her and with her eyes communicate when she uses her feet on pedals also adding guilt to it and seeing what she’s doing to her while she does that