Is the prayer of one who prays sitting, making his bowing lower than his prostration, and slightly bending his back forward when sitting between the two prostrations while saying "My Lord, forgive me," and during the Tashahhud, valid or void?

Whoever is unable to stand in prayer, or finds it difficult, should pray sitting. They should gesture for bowing from their sitting position, the minimum of which is bending until the face is level with the front of the knees, and the maximum is until the forehead is level with the place of prostration. As for prostration, it is like the prostration of one who stands, unless there is an inability. The gesturing for prostration must be lower than the gesturing for bowing.

And whoever gestures for bowing lower than for prostration has acted contrary to what is obligatory and must repeat the prayers performed in that manner, because gesturing takes their place in the absence of an excuse, and one must perform what is possible, and prostration is lower than bowing.

If the questioner bends her back slightly while sitting in prayer, in a way that is outside of normal sitting, then she must repeat the prayers performed in that state, because maintaining an upright posture in sitting between the two prostrations and in sitting for the tashahhud is among the pillars of prayer. However, if the bending is slight, then there is nothing upon her.