Sounds like her dad traded one addiction for another... that is common with those not in recovery.
Congratulations on being strong to break the cycle in your family. That is something to be proud of!! Your children need one healthy parent... keep your focus on being there for them.
A saying I've heard around here alot is... "I'll support you in your recovery, but not your addiction." I used this alot with my AH when he had relapsed and was actively using.
It is very stressful living with someone active in their addiction. YOU need all the support you can get... keep reading and posting! Have you tried Al-anon or Nar-anon
meetings?