Aborting under the advice of one doctor

Shalom rav,

I was just asked the following question, which I would like to present to you. The lady who asked me is pregnant in the 9th week of gestation. Two weeks ago, i.e. in the 7th week of gestation, an ultrasound was performed. It demonstrated that the embryo has had a heartbeat and was therefore viable. Now, two weeks later, a repeated ultrasound revealed absent heartbeat. The gynaekologist declared that an intrauterine death of the embryo has occured and recommended the lady to let an abortion be performed.

Questions:

1. Is it pertinent to rely on the opinion of only one gynaekologist i.e., is there an obligation to consult another specialist?
2. Is the absent heartbeat a halachically sufficient proof of death of the embryo? Or is only the case if proven on several occasions at different points of time?
3. Should the death of the embryo be thereby proven, are there any halchically specific features of such an abortion?

I would be very much obliged for an answer before Shabbos, since the lady in question is under considerable emotional stress.

Thanks in advance / kol tuv

P R