although very outdated here in the Netherlands you can find it looking in Dutch genealogy trees
it's the female form of Meindert (often was done: take a dutch male name, put -je or -tje after it and u have a female name: examples are Hansje, Arentje and Keesje)
what it exactly means im not sure, but 'Mein' (as stated in an other thread on this board) means 'strength'
there is an URL down this board somewhere in the post called "why is name still not added?" (remember?)
wait...i'll look it up for you