Well..."Important positions in the government" is an interesting way to phrase things. A few specific countries in Europe-England, Russia, Spain-allowed queens regnant, that is, women to hold the throne of a hereditary/familial (in Catherine's case) monarchy. You do not see women serving in Parliament, in the king's chamber, or on the city council. In a lot of cases, women aren't even legal persons-they can only sue in a court of law (to defend their property) or run businesses under a male guardian.

English law, unlike e.g. France, did permit women to inherit the throne. However, you'll observe that Edward Tudor was the youngest of his siblings, but Mary and Elizabeth were only eligible to rule after their younger brother's death-men came first. Because of the religious situation in Europe at the time, it can be a little challenging to separate out the polemic against Mary and Elizabeth's reigns on a gender and religious level-in fact, the two issues became so intimately interwoven in their case, it shows exactly how problematic a woman ruling men was seen to be. (Given that Europe was tearing itself apart over religion at the time).

You see this most clearly, in fact, in Edward's attempt to pass the throne not to his Catholic older sister Mary, but Protestant cousin Jane Grey. But she was still in the family line of succession. That's the key.

The idea of a quasi-mystical "ruling line" was real. In Russia, Catherine the Great's predecessor (well, before her husband), Empress Elizabeth, apocryphally maneuvered her way into the throne by marching into the palace to stake her claim based on bloodline. Indeed, would you deny the throne to its rightful family heir, and leave it in the hands of usurpers?

As far as actually ruling, the queens regnant of early modern Europe adopted massive publicity campaigns, seeking ways to legitimize their rule as women. Isabella in Spain (that Isabella) built up a public image based on the iconography of the Virgin Mary, which was interesting when she had kids. Elizabeth's Battle of Tilbury speech tried very hard to respond to the criticisms of women's weakness, and portray her not as a ruler but as a king at war.