First of all WELCOME and GOOD FOR YOU! for reaching out to this site and sharing.
Secondly, WOW we have the same stepdaughter?
Sounds like you really want to help... I want to do the same for my step daughter who has said she has a problem.
Usually the decent ins programs have coverage for treament. They do an evaluation and will recommmend either outpatient or inpatient treatment depending on the severity of the case.
Its tough though knowing when to step in or "if" to. In our case, we are waiting for her to come forward to us and ask for help rather than chasing her down. They wont really get better until they are ready to. If however she has told her mom "I want to get help" then I think it would be appropriaate for her dad to tell her he would be willing to take her for the evaluation. Try not to set any expectations for how it all should go though, becasue its really up to her and may take a while.
These are my opinions and experience only. Others will have their persepctives!