1999 Plymouth Breeze Wheel cylinder and pads question

I have recently replaced the wheel cylinders, drums, shoes and spring hardware in my mothers 99 breeze.

After driving for about a month she tells me she is starting to hear some noise from the pass rear, The rear brakes were really worn down with lots of dust covering the inside of the wheel, also the wheel cylinder came apart.

Drum assembly was rebuilt(both sides) after about two weeks this time she calls me and said her wheel was smoking. This time the drivers rear had the problem(wheel cylinder came apart) but there is still 1/2 of the pad material left which I know is not normal. I was able to but the cylinder back together
and had the thought of my moms wheel catching on fire! So I let her use betsy my 97 sable so she can get back and forth to work.

Basic problem is rear brakes are wearing down fast and wheel cylinders are coming apart.

I am not sure how to tell if the master cylinder is the problem or the proportioning valve. Brake lines look good cannot see any obvious leaks, any definitive way to check the lines?

Any help would be appreciated and thank you for your time.

P.S. I would Definitely donate 10 dollars if I could get this to stop happening again