Overdose - Methadone and Cocaine?

[inozip]

I'm doing research for a client whose daughter snorted an unknown combination of Methadone and Cocaine. At least this is what showed positive in the drug screen.

She went into respiratory arrest and ended up on a Narcon drip in the hospital for 2 days. She was labeled a possible suicide attempt and overdose.

My questions are this: Is this common to snort this combo? How much would normally be insuflatted? Would vomiting be a side effect? Why would anybody do this? She has a history of headaches and pain...

As you can guess, I don't do any drugs so I am not familiar with this at all.

Thank you for any information