Remove Imported GEDCOM - Help!

I made a huge mistake and downloaded a GEDCOM.I don't know how I did it but it went into my master file instead of the new file I had set for it.
Now I realize that this person doesn't do research but collects names.My file is so messed up!She has parts of my family but others who I know have no place in my records.
What is the easiest way for me to get her records out?
Can I do it by the date of the import?
Thanks for your help,
Debbie