Lady Seren - Stronghold 2 AI Lords

Lady Seren is a very poor opponent. To start with, she only ever builds the exact same Castle. And it's not exactly a good one - in fact I'd consider it one of the worst. Containing a massive hole in its wall with only killing pits and man traps placed over it for protection, this castle allows anyone to essentially walk straight in and get to her keep providing they have the numbers. Her Granary is placed outside of even this which means you can damage her economy very easily. Her Castle contains a single poorly placed tower with walls which are constructed even worse, in most places containing just a single line of stone.

Seren's harassing tactic is to spam as much Light Cavalry as possible and persistently send it over. This trick does work if your castle is very lightly defended as they can do damage to your buildings. However, with a decent number of ranged units in towers or upon your walls, you can easily crush these constant attacks with very little if any damage. Light Cavalry is fast but at the cost of being extremely vulnerable to missile attack. I also recommend placing an extra stone wall around your buildings, just in case your missile troops do somehow miss a few cavalry units which attack you.

Lady Seren takes probably the longest time out of any AI lord to create a sieging army. This army mainly consists of Armed Peasants, Swordsmen, Archers, a few spearmen and more Light Cavalry. She creates several catapults and tries to break down your walls, but providing you have a good defence they should not pose any kind of real threat, hopefully being destroyed before they even get into range. She will then attempt to send in Laddermen, but these will almost certainly do nothing. I recommend placing several towers and adding Crossbowmen in them as they will be able to quickly decimate any approaching enemy troops.

Taking another strategic look at her castle, there are also one or two pitch ditches placed, but other than this it's an easy ride to just walk straight in. Taking out the tower with a Trebuchet or two would be a good move before sending in any troops, although this doesn't make a massive difference if you attack with fairly mobile troops, such as Macemen for example.

Tip: When attacking Seren's castle and using the gap in her wall, use Armed Peasants to trigger the traps before moving in with your real troops. Killing pits unlike man traps are triggered by a certain weight rather than whenever a unit walks over them, so group them around the killing pits in order to trigger them.