I would have got her RHD gene sequenced earlier in her pregnancy, so that I would have a better idea as to whether she required anti-D immunoglobulin.
If she turned out to be (potentially) a Partial D, or a Weak D other than Types 1, 2 or 3, I would give a double dose of the normal dose of anti-D. Anti-D immunoglobulin is still derived from humans, which means it is a "soup" of different anti-D specificities against the 36 odd epitopes, some of which would be expressed on the lady's red cells, and some of which would not. Therefore, some of the anti-D specificities would be adsorbed onto the lady's own red cells, but others would remain in her plasma, and would be "available" to react with the red cells of her foetus's red cells, and so would give her some protection against producing her own immune anti-D.