I'm so sorry, Melissa. The good news is that she's back at the soberhouse.
Yes, many/mosts addicts do relapse. I know with my difficult child, he had the pot problem and went to an Residential Treatment Center (RTC) for 4 months. Not quite 2 years later, he relapsed again, and went from pot to crack cocaine after about 2 weeks of pot.
Once again, Residential Treatment Center (RTC), but that time, it was for 10 months.
About 2 months after he came home after being drug free almost a year, he relapsed for a weekend. He ended up calling us, scared to death. He said it wasn't fun anymore; it was just scary.
As far as I know, he has not drugged since.
It can be done. She has that gorgeous little baby to hopefully inspire her to clean up her act and stay sober/drug free this time.
Many hugs to you. I know how devastating it is when you think they're clean and they relapse. You go through that pit in your stomach all over again.
Deb