  The center of the Milky Way contains stellar populations spanning a range in
age and metallicity, with a recent star formation burst producing young and
massive stars. Chemical abundances in the most luminous stellar member of the
Nuclear Star Cluster (NSC), IRS 7, are presented for $^{19}$F, $^{12}$C,
$^{13}$C, $^{14}$N, $^{16}$O, $^{17}$O, and Fe from an LTE analysis based on
spherical modeling and radiative transfer with a 25M$_{\odot}$ model
atmosphere, whose chemistry was tailored to the derived photospheric
abundances. We find IRS 7 to be depleted heavily in both $^{12}$C (~-0.8 dex)
and $^{16}$O (~-0.4 dex), while exhibiting an extremely enhanced $^{14}$N
abundance (~+1.1 dex), which are isotopic signatures of the deep mixing of
CNO-cycled material to the stellar surface. The $^{19}$F abundance is also
heavily depleted by ~1 dex relative to the baseline fluorine of the Nuclear
Star Cluster, providing evidence that fluorine along with carbon constrain the
nature of the deep mixing in this very luminous supergiant. The abundances of
the minor isotopes $^{13}$C and $^{17}$O are also derived, with ratios of
$^{12}$C/$^{13}$C~5.3 and $^{16}$O/$^{17}$O~525. The derived abundances for IRS
7, in conjunction with previous abundance results for massive stars in the NSC,
are compared with rotating and non-rotating models of massive stars and it is
found that the IRS 7 abundances overall follow the behavior predicted by
stellar models. The depleted fluorine abundance in IRS 7 illustrates, for the
first time, the potential of using the $^{19}$F abundance as a mixing probe in
luminous red giants.
