A lot of questions.
First, someone can be named in two different lawsuits if there are two different copyright holders or two different copyrighted works involved. If the woman illegally downloaded two different movies owned by two different companies but she downloaded them using the same computer at the same IP address, this same IP address and this same woman can be named as a defendant in two different lawsuits.
You will want a forensic image of your computer hard drive to preserve all evidence of the contents of your computer. Tampering in any way with your computer's content can result in a jury finding you guilty of copyright infringement based on evidence of altering and
absense of evidence on your computer. Seems odd, perhaps, but this is how it works.
Claims of spoliation of evidence are often made in computer-based infringement cases, and adverse sanctions will be sought by the plaintiffs against any defendant shown to have "messed with" his computer after the defendant has been notified of an infringement action against him and the need to preserve computer contents.
Many infringers will attempt to delete all evidence of illegal downloading, not aware that forensic experts today can detect these attempts. Writing over files is one way in which infringers try to hide evidence of illegal activity on their computers.
When a file is deleted, it does not disappear forever from the computer. It still takes up space on the computer until this space is needed for other files. When this space is needed for another file, the file that is "written over" the deleted-file space may not use up the entire space devoted to the deleted file. There are often "fragments" of the original deleted file left behind. These fragments from the original file can be used to show an illegal download.
As for expectations by a plaintiff and the courts in a copyright infringement action, you can check out Federal Rules of Civil Procedure, Rule 26, General Provisions Governing Discovery; Duty of Disclosure, and FRCP Rule 34, Production of Documents, as it relates to electronically stored information, and FRCP, Rule 37, Failure to Make Disclosure or Cooperate in Discovery; Sanctions.
Mass discovery, by the way, is being used by copyright holders to determine the real identities of those who have illegally downloaded copyrighted material. These mass discoveries target the ISPs that hold customer account information and do not target the individuals who may have illegally downloaded the material. Once the identities of the "John Does" have been revealed through the subpoenas issued on the ISPs, individual infringement suits can be filed against the identified downloaders (generally after notices of settlement are distributed to the Does by the copyright holders, offering these identified Does the opportunity to avoid costly court actions by settling the matter for X amount of dollars).
There were resources posted not too long ago for posters who were served with notices of infringement. If you use the "search" feature at the top of the page and enter "West Coast Productions" into the "key word" box, several threads will appear. The one titled "Illegal Downloading" provides resources you may find helpful in your situation and browsing through all of the other numerous threads posted can help educate you on what you face or could face.
Again, I advise that you consult with an attorney in your area, Justaskingq, to see what steps are necessary for you to take at this point, and to see exactly what you can and can't do safely with your computer until the infringement matter is resolved.
Good luck.
