You don't need a new libname, you can use any libname that you have already created.
Let's suppose you already have a libname named FRED, and you want to create this new data set inside libname FRED. Then something like this works, it creates a new data set named FEMALES_ONLY in libname FRED. (That's what the two-part name indicates, FRED.FEMALES_ONLY is the data set FEMALES_ONLY in libname FRED). For example:
data fred.females_only;
set yourdatasetname;
where gender='F';
run;
But even the above is not necessary, assuming that your colleague has read access to your existing libname. you can send this person the LIBNAME statement, placing ACCESS=READONLY at the end, and then this person can do whatever he or she or it wants, you shouldn't have to subset the data for this person.
libname FRED "yourfoldername" access=readonly;
--
Paige Miller