If she had been offered and refused an honour you would not know unless she went public about it.
Just because young people dedicate much of their lives to training to attain excellence in sport or anything else should not count towards any honour, for every one who succeeds there are many hundreds who put in as much effort for as long and never hit the highest level. Should they get knighthoods etc?
I think the highest level of honours; knighthoods, damehoods etc should go to those who have performed at a consistently exceptional level, over a extended period of time, or have followed their sporting excellence, though brief by high achievement in another or related field. And I do not consider that anyone under 35 is likely to fill this criteria.
If you have won a Gold Medal at the Olympics, or become a World Champion in a sport, that was always your aim and is recognition enough of your prowess. Do it multiple times over 5 or more years and follow that with another 5 years, dedicated to helping others do what you have done, form a charity and be involved with it, like Mo Farrah has done, I understand and after 10 years of such exceptional dedication and, yes, you have earned your knighthood. There is nothing to stop you being awarded a lower level of honour, CBE, OBE or whatever
I just think that the higher echelons of any honours system should go only to those who have given exceptional service in any field for at least 10 years, preferably 15.