Thanks guys!
Indeed I thought of painting, but I'm not too fond on manipulating pictures up to that point. If my previous background would be at least 6 x 4.5cm format, and my enlargements would have been pretty big, perhaps I would have accepted painting her face in PS, in accordance to what would have been burning/dodging in film. But since my film background is 24 x 36mm format and my enlargements have not been big enough to justify burning/dodging, I try to stay as close as possible to that landscape. Hence, I tend to avoid PS retouching and limit myself to Lightroom.
In regards to this photo, I arrived to the same conclusion as both of you -the shadows can't be reduced signifantly while maintaining contrast-. Somehow, the B&W conversion, even with the yellowish filter added (I imagine a Wratten 3 mixed with an 81A or B), makes her -to my eyes, of course, this is an absolutely subjective perception-, older. Of course, applying enough filtering to bring back life on her face simply blows lights on the rest of the picture.
DanielJ, I'm amazed by your conversion, indeed it is really good. My skills in PS retouching aren't up to the task...
I would have liked to take the same picture with an Agfa APX 100 or 400 film, to see how it rendered on it, and which would have been the opportunities at enlarging to "fix" (between inverted commas because as I said, it is subjective if it is nice or not, this is not a technical problem) the shadows under her eyes.
I do agree with McQ that the yellowish filtered B&W version is indeed nice and, short of painting the photograph, it's the best case with a standard conversion. I achieved more or less the same results (Lightroom has a very nice channel mixer), but I still didn't like it too much. Perhaps if the picture would have been B&W from the beginning (I'd kill for a sensor that mimics Agfa APX 100 and a developing formula for Lightroom that resembles 13.5 minutes in D76 1+1

) I would't find this issue. Now that I think about it, it is very probable. But well, in the meantime I'll stick to McQ yellowish filter conversion, I think short of painting is the best that can be done.
People, thank you very much sincerely.
Cheers,
Sebastián.