If that was your father's desire, then it is fine. If she was exerting undue influience, then it is not fine.
A lawyer could allow her to sit in on the meeting if your father desired that but the lawyer should ask her to leave at some point to talk with him privately. Again, you are trying to avoid undue influence.
Was this a long term girl friend? I could see them getting defensive if they were hiding something, but I can also see them getting defensive if the final will was just as your father wanted it but they were afraid the children would contest it.
I do not know if this answer would be different for the state involved here if it is IA but in most states I know of this is not against any law or necessarily unethical. It may effect confidentiality between the client and attorney but that does not make it against the law or improper. As a general practice many attorneys would suggest at least having some time alone with a client if there is an inclination that a person is influencing but I know of no specific statute or rule prohibiting a close family member or friend from such a meeting.
This is not legal advice nor intended to create an attorney-client relationship. The information provided here is informational in nature only. This attorney may not be licensed in the jurisdiction which you have a question about so the answer could be only general in nature. Visit Steve Zelinger's website: http://www.stevenzelinger.com/
What's the value of the probate estate? If she was really trying to get his assets why didn't she just have herself put on them? Did she have a power of atty over your father? These questions and others must be answered by a lawyer of your choosing. Good luck.
Legal disclaimer: This answer does not constitute legal advice. I am admitted to practice law in the State of Missouri only, and make no attempt to opine on matters of law that are not relevant to Missouri. This answer is based on general principles of law that may or may not relate to your specific situation, and is for promotional purposes only. You should never rely on this answer alone and nothing in these communications creates an attorney-client relationship. less
It sounds like you have a few red flags. But the biggest problem is that you need very compelling evidence of undue influence in order to overturn a Will. If you have facts where your father was losing his capacity and was susceptible to undue influence, and you can prove that, you may have a shot. But most courts are extremely reluctant to overturn a Will. You will have a major uphill battle.
*** LEGAL DISCLAIMER I am licensed to practice law in the State of Michigan and have offices in Wayne and Ingham Counties. My practice is focused in the areas of estate planning and probate administration. I am ethically required to state that the above answer does not create an attorney/client relationship. These responses should be considered general legal education and are intended to provide general information about the question asked. Frequently, the question does not include important facts that, if known, could significantly change the answer. Information provided on this site should not be used as a substitute for competent legal advice from a licensed attorney that practices in your state. The law changes frequently and varies from state to state. If I refer to your state's laws, you should not rely on what I say; I just did a quick Internet search and found something that looked relevant that I hoped you would find helpful. You should verify and confirm any information provided with an attorney licensed in your state.