Geitz had been holidaying in Central Otago after finishing up her commitments with the team following the second test in Auckland.
The Diamonds desperately missed Geitz's ball-winning abilities and composure in the second half in Melbourne as the Ferns overturned a seven-goal halftime deficit.
But Alexander said the star defender has been called back into the team to cover injuries to senior players Caitlin Bassett and Renae Ingles (nee Hallinan), who was to be stand-in captain in Geitz's absence.
While Australia already appear to comfortably have the Constellation Cup locked away in the trophy cabinet for another season regardless of tonight's result, with the Ferns needing to win by at least 14 goals tonight to claim the silverware, the decision to rush Geitz back into the line-up signifies the Diamonds' intent.
A drawn series would be as bad as a loss for Australia.
Along with the unscheduled appearance of their captain, the Diamonds will also be bolstered by the likely return of Bassett, who sat out the second half in Melbourne with what was loosely described as "foot injuries".
Some saw the decision to bench Bassett in the second half as Alexander seeking to make a statement by beating the Ferns without their star shooter.
If that was her motivation, then the ploy badly backfired, as Australia gave up a seven-goal halftime buffer in a quarter.
Alexander later admitted they are not the same side without Bassett.
"We're really hopeful [Bassett] will be able to play, we certainly need her out there at the moment," she said.
Stung badly by the loss in Melbourne - just their second defeat to the Ferns in 14 outings - Alexander said her side are determined to atone in Perth.
"We're absolutely devastated we lost that game. You don't purposely go out to lose a test match when you're playing for your country, so we're really annoyed."
That sort of passion and emotion should be more than matched by the Ferns camp, with the match expected to be the last outing for a host of senior players and coach Waimarama Taumaunu's final test.
Constellation Cup
Fourth test: Silver Ferns v Australia. Tonight, 11.45pm. Perth Arena