Neggy's got better physical strength though, as required for a boxer, it may not be at the same level as a male would be, but even a female boxer has to be physically strong. That gives her an advantage over Reina, Reina's trained to be fast, she has average physical strength but not at the level of a trained boxer.
Her advantage would be her speed, if she can keep on the move and try to wear Neggy out then she could have a chance, but only if she can avoid any serious punches. Her healing rate has it's limits, the more the damage and the more she heals, the faster she becomes too exhausted to keep going and will either drop into a coma to save her higher brain functions or her medical requirement will kick in to do the same thing, leaving a pretty helpless toddler in a pile of clothing.
It would be an interesting fight to see, both have their strengths and weaknesses and both have an upper hand over the other, but only if they can make use of that upper hand at every chance.