Like when learning many musicial instruments, it is very common to get some discomfort when learning to play.  It takes a while to develop strength and suppleness to reach difficult chords on a Guitar, for example.  Because whistles seem to be simple instruments, many people expect to be able to pick up and play them straight away, but there is some practise and play-in time required and that can lead to some discomfort before hands and muscles devlop to overcome initial challenges.
Some discomfort when learning can be expected irrespective of hand size, age or gender, but it is perhaps a question that more often comes up for women who suspect smaller hands might affect ability to cover the tone holes, which is understandable. Women tend to be more supple than men however, and we don't actually see any correlation along gender lines.
In the several decades we've been making them, we have had very few Low D's returned because of hole spacing   ...and it's extremely rare that we get a smaller/higher key of whistle ( < low D)  back for this reason.
Generally, be prepared to put in a little practice and, unless you are very unlucky, you should be fine.  Using the technique known as the 'pipers grip' can help.   You can read more about this here.
Here is a datasheet for a mk Pro D
Here is a scale drawing of an mk Pro D.  You can print this out to scale [make sure you have scaling turned off on your printer]  and wrap it around another whistle or something cylindrical to get an idea of finger-spacing.
If you were to have issues then make use of our returns policy.