There's no way the fluid is boiling, unless she's racing or riding them down huge hills. There is a leak in the system, check all the hard line connections, and as many of the hard lines as you can, (some run through the car, but those shouldn't have any corrosion or bending issues), also it's a good idea to replace the flexible rubber lines and inspect the location where they connect to the hard line and the calipers, after 12 years they are bound to have cracks, this is the most likely reason the system is getting air in it. It is possible the lines have cracks small enough to let air in but not fluid out. A caliper with a bad seal could also be the problem. There is no reason to try and bypass the ABS system. The only other thing I can think of is something I did once that was pretty stupid, I didn't have the bleeder screwed back on tight enough and fluid was leaking out. Might be worth checking too