If you issue an ultimatum and do not follow through if the contingency is breached, your friend will realize there are no consequences she needs to be concerned about.

For example, if she continues to imbibe but agrees to seek help because she realizes she has a problem, will you leave her because of the ultimatum? Or, will there then be another ultimatum: Get help now or I will break up with you? What if she gets help but continues to drink?

My thought is that ultimatums restrict flexibility. You have let her know how you feel. Wait and see how see responds. If it is not working for you, then you have a choice to make.

Good luck.