Lobke is Dutch, it's a feminine pet form of Lubbe, which is a short form of names containing the element Liaf
"dear / beloved" (ex: Lieven
) or the element Liud
"people" (ex: Ludger
I have an obscure family member with this name, it's her full name, in the Netherlands it's very often that chidlren are given pet / short forms as full names. So it doesn't mean that just because Lobke is a pet form, the girl has another full name.
Anyway some possibilites for a full name are: Lobrichje, Lubrichje, Lubarta, Lubina (but these are all much rarer than just "Lobke", which is already unusual in itself).