The most important thing to look at is whether or not your phone wire going to the jack has 4 wires. Also, you need to make sure that the female receptical has four little bits of copper showing. Typically the green/red pair is line one and is the middle pair and the yellow/black pair is line two and is the outer pair on the connector. If all your wires end up in the same location in the basement then you can hook up the new line to your yellow/black pairs and then hook up the jacks correctly. You might need to get new jacks if the ones you have aren't up to the task. If you need new jacks I would get the ones with two recepticals, one for each line, but usually you don't have to do this. You can just use one of those splitters at radio shack that have one male and two females.
If you have a two line phone then you just make sure that you are using a four pin wire (yellow/black and red/green wires inside) and that the male connectors on either end have four pins, not just two. Then you will have both lines on your two line phone. If you only want her to have her own line then you wire the yellow/black pair to the middle two pins and it will appear as the regular, and only line on a one line phone. You sometimes need to do this for computer modem lines too because most people use line two for their computers, but the modems only read the middle pair, which usually has red/green line one. It is not correct to wire line two to the middle pins and line one to the outer pins at the jack, but sometimes it works if you want a modem on line two or a one line phone on line two. Hope this helped.