I had to do a similar repair for my Chloé who had not travelled well from the north of France.
It was easier as being on the top of the boobs it was possible to inject silicone from the side under the arms. The syringe was very stiff. I heated up the syringe and the silicone to make it flow better but it still needed a lot of force to push in.
This injury is more difficult as being between the breasts it's the other side from under the arms. Some people recommend going in through the nipple.
Chloé's injuries were terrible
but the repair went well
and in fact the slightly less full breasts are more realistic than on Chloé's sister in England.
I used RT50 silicone, from memory with a 1.5% catalyst rather than the 2% suggested and letting her warm up in the sun outside enabled it to cure faster. Another doll expert recommends bathroom sealant although in quantity I think that could be rather stiff.
Something I have come to like enormously for repairs is Permatex flowable silicone for windshield repairs. It's really great and it flows. With my experience I would make a clean cut in the side of the breast, at an angle going upwards from the crack and I'd use Permatex through the thin nozzle supplied (3mm) and then let it cure pushing the cut together with cling film over the top or sellotape. Let the cut not have enough glue in it first and then a day later put another drop in the cut. By the way, wipe the inside of the cut with a cotton bud with acetone before gluing. I did a repair on Aira the other day on her shoulder which is completely invisible. Completely . . . Invisible.
So this problem is not going to be terrifying to rectify and
Chloé sends a kiss to Dani saying that she'll get better soon.
Best wishes
Harem