interestingly enough, I ran into a problem with my 900 MHz cordless not long ago. It was placed near my phone jack, which has a splitter as well, except our splitter is for two phone lines. the phone would often cut in and out, then eventually kill its signal.

you should try moving the phone to another phone jack, far away from the problem area, and see if the problem persists.

and I don't quite understand your description of her DSL setup. All DSL configs I've seen have two jacks--one for voice, one for data--no splitters (though an external splitter may be accomplishing the same thing that the two-jack wall mount is doing). If you don't like the splitter, ask for the separate voice-data ports via wall jacks, not splitter.