Completed it.
Strategy:
1. Split the "battle" in the centre with the counter inf moving to assist the north. King Edward will join the south.
2. Northern forces to withdraw to defend, while the southern forces are to assemble around the castle to prepare to engage.
3. The clumped south steadily advance while the north advances a turn or two later. Use Edward IV's ability to pick off enemy mobs from the south.
Lean against the edge of the map to reduce exposure.
When the two gens fall, there will be a morale boost for a friendly troops.
4. The enemy spam will slow, especially when the southern city falls (taking either frontal city triggers the cav charge). Defend the city, regroup and prepare to advance just like before.
Northern troops are to move quickly to take and hold the northern city.
5. Regroup any wounded troops (use war gears or switch troops). Quickly rush the last city. Be careful not to let her pick off key gens.
Completed all of Easy mode without Drums, IAPs or Talent. (Beat Buckingham's Rebellion right after without evacuating him in time).
Gens used:
(Northern group)
- Justinian (2× melee inf)
- Narses (2× counter inf + ranged inf)
- Subutai (2× ranged cav + counter inf)
- Harald Hardrada (3× melee inf)
- Theodora (counter inf + 2× ranged inf?)
- Robert the Bruce (3× counter inf)
(Southern group)
- Reinforcement Alfred (Tang melee cav, Maodao, and Noble Cav)
- Belisarius (2× melee inf?)
- Murad II (2× melee cav)
- Timur (melee inf + 2× ranged inf)
Lvl 24 common troops turned the tide. Specifically, tiers 1-2 and 4-5, except for tier 4 cav units.