I have done this in a reverse situation...
and told the guy, I would like to date you
but want it to be one on one, and not a group
date.
If she says no, perhaps she is not ready
for this level of dating and you may have
to make some other choices. She may also
find it easier to tell her friends that YOU
prefer to spend time with her alone on a date
if their group dynamic has included her in
everything. I have been there too but hey,
my friends got over it...