Sounds funny, really...how to detach from someone you live far away from but I am in the same position and oddly geographical distance makes it harder in some ways.
I speak to you in part as someone who has been in recovery from alcoholism for many years and worked with many other alcoholics who have gotten sober. If your mother is in and out of recovery it means unfortunately that she hasn't had enough pain yet to get really serious. She knows what she needs to do,she just doesn't want to do it. How much pain it takes, is unfortunately widely varying. Alcoholics can have a tolerance for a huge amount of pain and most go to their deaths without getting sober.
The best thing that you can do for her is get out of her way and not help her in ANY way until she makes the decision that she is serious about getting help for herself. It is hard to see,but important to know that they ways that we try to help them actually hurt them.
Recovery for an alcoholic involves a whole lot more than not drinking, so I wouldn't make whether she is drinking or not the issue. My Mother periodically quits drinking...mostly to convince herself that she isn't an alcoholic. I have cut contact....and will not be back in touch with her unless she gets into a solid RECOVERY. I will know that she is by major changes in behavior faaaaaaaaaar beyond not drinking. I'm not holding my breathe...my bet is that she will die a drunk.
IMHO best thing that you can do for your unborn child is to take good care of yourself in every way that you can. He/she is your future/the future....one that you can choose to create in a totally different way than in your FOO. No child deserves to be born into the kind of unhappy chaotic emotional environments that alcoholics create.
There are times in life when it is appropriate to be selfish. Pregnancy is one of them.