Addiction is addiction, whether it's alcohol or heroin. Both drive people to do insanely stupid and dangerous things like your fiancee did. If it makes you feel any better, though, she can go to AA meetings when she gets out, which are focused strictly on alcoholism. There are slight differences in the EXPERIENCE of alcoholics and those addicted to other drugs--for instance, you don't have to go to dangerous parts of town and buy your substance from someone who might be carrying a gun, but believe me, alcoholics can debase themselves just as effectively as other addicts. Alcoholics are not "better" or "worse" than someone addicted to drugs.
This is another bit of that "terminal uniqueness" we keep talking about. Your fiancee is a DRUNK. That's the bottom line. People who just "drink too much" don't drink and then get behind the wheel of a school bus. They might pour themselves too many drinks in the evening, or have a tendency to overdo it at a party, but drinking during the day when you have responsibility for the welfare of children is something that sane people do not do. Alcoholism is a form of insanity. Not in the legal or medical sense--but for all practical purposes, the alcoholic is insane when it comes to drinking.
Alcoholics and other addicts have more in common than they have differences. And alcoholics in general--whatever their financial or social circumstances--have more in common than they have differences, when it comes to drinking. I've heard people share at my AA meetings who have done hard time in prison (one person was on death row before capital punishment was abolished in NJ, and another did time for killing someone in a fight), and when they share about how they FELT about alcohol--what it DID for them--their experiences mirror my own. I didn't drink in the same places they did, but I felt the same way about my relationship with alcohol.
And, yes, I think you would be VERY wise to make good use of this time when she is in rehab to educate yourself about what you will be dealing with when she comes out. If the very best happens, and she decides to stay sober, early sobriety is very challenging for both parties in a relationship. And if she DOESN'T stay sober, you need to know what you can expect then, too.