Miranda is not usually a complete defense to a DUI arrest though it can muck it up. Implied Consent is very different. Failure to give implied consent can be a complete defense in a suspension hearing, but typically you will find law enforcement will simply lie about it making it a credibility contest. But I would not hang your hat on Miranda.
Mr. Michaels is correct that the implied consent issue is the more important issue for the DOL hearing. However, your friend needs an attorney who can represent her in both her felony and administrative hearings. She should contact my office for her free consultation right away. 425-424-9401.
That is a fairly common set of facts. Remember that the public defender does not represent her at the DOL hearing. She has 20 days from the day of the arrest to request a DOL hearing, or it is waived and she will be revoked for at least a year. Lack of implied consent is a compelling issue, but she will usually have a higher chance of winning if an attorney represents her.