Brakes

There are a lot of variables we do not know. Most importantly, was the reservoir allowed to run empty and does the vehicle have anti-lock brakes? If it has ABS and the reservoir ran empty, there is likely to be air in the hydraulic controller. On most vehicles that can only be bled out with a scanner to command the computer to open two valves so those chambers can be bled. That has to be done with two bleeder screws open so the air can flow to them.

If bleeding was done with a helper and they pushed the brake pedal all the way to the floor, it is possible the master cylinder was damaged. Typically that results in a slowly-sinking pedal, and that often does not show up until two or three days later.

This sounds like the master cylinder is damaged and needs to be replaced. Here is a guide to help you see what you are in for when doing the job:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Please let us know what you find.

Cheers, Ken