OK, so there is difference between being charged with a DWI .15 and being CONVICTED of a DWI .15. If you are CONVICTED of a DWI .15, you are facing mandatory jail time along with a few other serious consequences which your lawyer must discuss with you. This is a case where you absolutely should NOT waive your right to counsel. Depending on the facts of your case, you may be able to get it dismissed at trial OR even if there is enough to support a conviction, perhaps your attorney can convince the commonwealth attorney to strike the .15 on the charging document and amend it to a .14 or lower, making this a non-mandatory jail case (assuming it is your first DWI and there are no additional aggravating factors) as a condition to a plea of guilty, if that is what your attorney advises you to do. Hire an attorney (or get court appointed counsel or a public defender) and explain all of the facts to him or her. They will discuss any and all defenses with you. If it turns out there are no defenses, they will tell you how to prepare for court (ie, what proactive action to take prior to court, such as community service, asap, letters of recommendation, independent alcohol evaluation, etc) in an effort to get the best possible outcome in negotiating with the prosecuting attorney, hopefully to break the case down by .01 and take you out of the mandatory jail time.
If you are qualified for a court-appointed attorney or a public defender, you should not pass up the opportunity to at least meet with them and give them an opportunity to defend you. Most court appointed lawyers are also retained lawyers and if they are devoted to what they do, they will not short change you but rather, fight tooth and nail for you with the whole of their heart. If after meeting with them, you decide that this doesn't hold true for the specific attorney that was assigned to you, then you can hire your own attorney as long as the timing is appropriate. If you are fortunate enough to have been assigned a public defender, again...you are getting an attorney who has devoted their entire careers to a cause they believe in. I can tell you from personal knowledge, the Public Defender's office in Fairfax is TOP NOTCH and if you were charged in Fairfax and were assigned to that office, you would be getting outstanding legal representation--that money can't buy you. Again, if you are qualified for state supplemented assistance, do not pass it up.
As others have already said, if convicted, she could face significant active jail, especially with a history and back up time if she is on probation on the prior charges. Even if she was not convicted on the prior instances, unless the cases were expunged, the prosecuting attorney will know about them and likely push for jail. If you are friends with this person and have strong reservations about filing charges, perhaps you should talk to her about her actions or urge her to get some help before filing charges. If you decide to file charges, remember that once the ball gets rolling , it is the commonwealth's case---not yours. You would be considered the victim and if you change your mind about prosecuting, while most commonwealth attorneys would nolle pross, there are some commonwealth attorneys who would likely still pursue the case and subpoeona you as a witness. Be certain that you want to move forward before doing so. The commonwealth's office will appropriately expect you to assist them. I wish you all the best.