Usher's Ex-Wife to Aunt: Say It To My Face!!! How'd My Son Nearly Die On Your Watch?

Usher's ex-wife has one serious
question before her emergency
custody hearing today -- how the hell
is it possible to let a 5-year-old nearly
drown if you're supposed to be
babysitting him? -- and only Usher's
aunt can answer it ... but she's
nowhere to be found.Sources close to
the situation tell TMZ, Tameka
Raymond attempted to serve Usher's
aunt Rena with a subpoena to testify
at the custody hearing today -- where
Tameka will argue she deserves
primary custody of her and Usher's
two sons -- but Rena couldn't be
tracked down.We're told Tameka
wanted Rena at the hearing so her
lawyers could ask about what led up
to the near-drowning of her 5-year-
old son on Monday ... when Rena was
supposed to be watching him ... but
without the subpoena, Rena doesn't
have to show up.Even without Rena,
however, Tameka has plenty of ammo
to fight for custody -- and we're told
her biggest weapon is that there was
no drain cover on the pool the day
Usher Raymond V nearly drowned.As
we reported, the 5-year-old got his
arm caught in the drain and nearby
contractors had to dive in to save him.
Rena called 911.Usher currently has
primary custody of the ex-couple's
two sons ... but Tameka hopes to
change that today.