Using a NoDrop chance of 19/68 in /p1 for her item TC, we can determine how often her 5 item-slots will fill up, and eliminate the chance for 2-3 runes to drop instead of just 1. Since only 5 items can drop, ther is always at least one pick left for a rune to drop, assuming that the rune TC's dont all roll NoDrop. This means that on higher /players settings or in a fuller game in multiplayer, keys/items have a higher chance to drop, and runes have a much lower chance. This would lead you to believe that The Countess can drop up to 8 items, but there is a hard limit of 6 items - and unfortunately the items have priority over the runes. This is also why up to Lo Rune is possible from countess, but is very rare - it would be a Lo dropping just like any other monster/SU drops runes. Note that she can technically drop runes as normal items outside of her Rune TC, so 4 runes is possible. First, she selects up to 5 items to drop, then she selects up to 3 runes from her special Rune TC. As you may know, Countess is special when it comes to drops.

Rune pickit list diablo 2