So why do you think she started doping a few months back? Why wasn't she doping when she was a 159 runner or a 67:30?
You'll have to ask her. But getting better results is quite an incentive. It's what drives most.
Sure so why didn't she dope when she ran 230+ or 6830? Why did she decide in the middle of summer to start doping? And if she was doping while running 6830, what magic new drug is slicing 4 mins off your HM time...
Why didn't she dope from 16? Or 18? Runners don't automatically dope (if they do), it is choice they make. There can be a bunch of reasons why they might make that choice. But the question you might ask yourself is: are improvements of the rate and magnitude some athletes make best explained by legitimate reasons or by their doping? Color me cynical, but when doping is such a pervasive feature in sport today it is easy to believe the latter.