For your magical needs you already have Tara, no need for a shaman.
Hell, you could go with fleshcrafting if you want a twist.
Give mom a monstrous/supernatural cock that could change length and girth to unnatural proportions. Or be like a dragon cock with scales, spikes or spines or whatever. But Ddos and Mls aren't horror games and Tara is not a Tsimizce nor a Cenobite.
As for a scientific approach, I think an advanced form of ivf with two eggs is a simpler solution to the problem then going with a futanari. You'd have to grow or transplant the entire apparatus. You are going to be adding organs instead of just replacing them, so it's going to be more difficult. You'd likely need to remove the clitoris completely. Reshape the rear end of the penis and attach the penis to muscles and maybe bones to hold it in place. Attach veins and nerves to penis, prostate and testicles. Maybe reroute the urethra. In the end you'd have to deal with a significant increase of testosterone. Which could have unwanted side effects.
I think showing the process could be at least interesting, if not exciting. Like in the trailer for
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. You could show the whole process from growing the organs in a lab through the surgery to mom testing her new equipment and maybe dealing with the side effects.
Mom having a Y chromosome would mean she has what, an XY pair or XXY? With an XY pair with an Y chromosome that has never gotten expressed, I don't think she would look like she does now, or even her body to work like it does. Because then she wouldn't have a second X chromosome either... And if she had an XXY combination, I think she'd have severe health issues. Could she even have kids?
I don't know what would be required for a natural occurrence of hermaphroditism in humans. Would they be even fertile? Would only one set of organs work? And I mean true hermaphrodites with both sets of organs. Not those few unlucky people stuck somewhere inbetween with not fully or correctly developed organs. Of course there are animals which are hermaphrodites. Snails, for one, if I remember correctly.
All things considered, if futanari is the choice, then magic is the better option. Most players probably wouldn't appreciate a montage documenting the whole ordeal of "manufacturing" one.
And if you say, "hey (mom) don't need to have both, a cock and balls are enough. (Why complicate things.)", I'd say I'd rather mom have both, because I prefer mom with a pussy or at least with both, then just with a cock and balls.