First she should make sure the filters they gave her are put on the phone line and not the DSL line. Leo thinks it's an issue with AT&T because the DSL tech tried connecting directly to the AT&T line outside of the house. The problem is that AT&T doesn't have much incentive to help her make this work because she's using DSL Extreme instead of them for internet.
Judith should try using a different phone in case of that being a problem. It also is possible that there's something wrong at the DSL Extreme router within the AT&T Network Operations Center, so she should press DSL Extreme to look into that.
Most likely though, it's on AT&T's end, and she'll have to convince them to fix her issue. Otherwise she'd have to look into getting a separate phone line for DSL.