Sissy needs surgery asap (chihuahua

Today my little chihuahua ran out the gate and got hit by a speeding vehicle who did even stop to look just kept on driving. Took her the vet and they are charging $1600 + for surgery $300 to keep her sedated .
Sissy is a very caring dog she loves to sleep on top of my black dame and are always chasing each other. She grew special bond between my 6 year old who has always has 6+ tantrums during the day but with her around it has gone down to maybe 1 . My son has speech delay and gets mad alot (he has been tested for autism but is only speech and motor skilled delay) but with Sissy he doesn't have to talk to her, he sits she comes running to his lap, they lay down to watch tv together, play outside together , they enjoy chasing chickens back into the pen. Almost all of my son activities are with her.