Oh now I get it. Your friend will let you use their account to host your web site.
Well, you need to upload the files to her web space obviously. And yes, her own pages will no longer appear.
However, some hosts offer multiple domains per account, in which case you can have a subdirectory under the main account and the second domain points to that subdirectory, thus allowing more than one domains to be live. Check with her host for more info.