Thanks for flagging up this series, mct, and the further info, Rocky. I'd not come across these books or this illustrator before, but, from a bit of googling I found some sample pages on line, and they look very interesting. I see that she's flying a de Havilland Comet in at least one of the books, which is a plus for old aeroplane nerds like me!
To me, Heuval's drawing and colouring style looks influenced by Willy Wandersteen as well as Hergé, though no doubt there are numerous Dutch and Belgian clear line cartoonists whom I don't know, whose influence may also be there in in the mix.
Let's hope someone like Cinebooks brings out the series in English one day. (Maybe I should try the French versions in the meantime, as my terrible French is better than my non-existent Dutch!)
I noticed when Googling that two Heuval-illustrated comic books not in this series -
Family Secret and
The Search - have been brought out in English.