The Blessed One of Rondra is one of the most played Blessed Ones in the Dark Eye. I'm going to look into that as well as dissect the ideas behind the Heavenly Lioness.
As with Praios, Rondra is basically worshipped in all the lands where the Twelvegods are worshipped. There are some peculiarities in some regions though, in Thorwal for example, she is less worshipped as a goddess than a force of nature and bringer of storms. In the South like Al'Anfa her domain as goddess is challanged a bit by the worship of her (in the canon of the Twelvegod belief system) demigod Son Kor.
The Aspect of Combat
Not unlike Praios, Rondra has an overarching aspect that stands above (most) other aspects as the overarching Idea behind the goddess. In her case that is combat. One of the names worshippers call her on is the "Sword and Shield of Alveran". All gods who embody the aspect of Combat have a different look at how a fight should be conducted. In Rondra's eyes a fight should be fair and at best not more than an honourable duel.
The Aspect of Bravery
Bravery should not be a surprising Aspect, how could you fight honourably without being brave? How could you stand up against the many enemies of the Twelvegods without being brave? Bravery is important to a fighter, especially one who wants to fight with honour or who fights the enemies of the Twelvegods. You don't need to be brave to fight ten against one or fight someone who's only armed with a stick while you hold a two-handed sword and wear full plate armour. You do need to be brave to go up against a skilled fighter while only being armed with their choice of weapon. And you definitely need to be brave to fight against the unspoken hordes of Demons who could (and sometimes did) invade the lands of Aventuria
Protection of the Defenseless
Now I have wrote quite a bit about honourable combat and what could be more honourable than protecting the defenseless? It is perogatory to the continued existence of the Twelvegod churches that they and their believers are protected. For this reason Blessed ones of Rondra defend other less combatative churches like the ones of Travia as well as the faithful who go on pilgrimages.
Honourable Duels
Honourable duels are a very important aspect in the church of the Lioness. Duels are even used to sort out arguments between priests. The idea of honourable Duelling and honorable combat goes so far that followers of Rondra (with a few exceptions) do not use bows and would never use a crossbow. Crossbows being the most despised non-supernatural weapons as they do not require (much) skill to weild nor does a crossbowman give his target a chance to fight back. Equally unhappy are priests of Rondra to recieve magical help, as the use of magic is not honourable. Not everyone can use magic and as such you have an advantage if you use it.
Thunder and Lightning
Rondra is worshipped as the goddess of thunderstorms, so many a wonder influenced by Rondra came with a downpour of rain and an accompanying storm. An important distinction to make is that the Lioness is not the goddess of rain as it waters the world and helps crops grow, but she lords over the destructive forces of great storms and over lightning and thunder.
Worship and Rituals
Rondra can be worshipped in multiple ways. Quite common are ritualistic duels between priests and mass services. One of the main components used in services to the Lioness is blood. Be it the blood of a sacrificial animal (most often a lamb or a goat) or self sacrificed blood. It is important to note however, that Priests do not give enough blood to weaken themselves but only scratch the palm of their hands. Another way people often serve Rondra is by serving the goddess more directly, as in fighting against the enemies of the Twelvegods or protecting pilgrims or other Priests on their missions. As with every church there are more or less conservative members. Some of the followers of Rondra believe that wizards and peasants can never be honourable, while others think that people can be honourable no matter their ability. There are even some Blessed Ones who use bows, this pretty much only happens in the region around the river Svellt as the region there has a high following of the god of the hunt Firun, and even though they use bows they use them only if it were honourable to use one. The only circumstance in which it would be honourable to use a bow is if the enemy is both not a human, dwarf or elf and they have surperior numbers.
I hope this helps with either playing a blessed one of Rondra or it helps to make it easier for you to incorporate the church in your games.
If you're curious about Praios, King of Gods and God of Kings, please check out the Post "Sun and Justice, Praios, the king of the gods