Here's my build for Grissenda. I call it *drumroll* Tanksenda! ... it's terrible, I know.
Her current statistics at level 20:
~~ le Build ~~
Cleave III Shield Expert III Resilience III
This is a build I made for my own unique playstyle. I'm not saying it's the most optimal one, it certainly isn't in terms of DPS, but I designed it so that Grissenda would keep aggro on the boss and mobs. This would work wonders with a backstabbing rogue.
Without Bash and Whirlwind (which are great skills), you won't have to worry about your enemies switching their focus onto you. That was really annoying to me, lol. Her pushing everything away also resulted in far away enemies being lured to us. Because of this I don't use those skills.
Anyways, I maxed out Cleave and Shield Expert first, prioritizing Cleave so that she still has great clearing potential. Resilience came last as it is an excellent skill against physical enemies.
~~ Other Ideas ~~
Bash is also a great skill for her if you use a sword & shield. This will stun even bosses for a millenia. The only downside is that all the pushing will reduce your dps (unless you're an archer) and it may lure more enemies to you.
Same goes for Whirlwind. Cleave > Whirlwind, but for serious aoe damage, get Cleave, Whirlwind & 2h Expert. She won't be a great tank but she'll mow down everything in her path.
Anyways, if you want a tanky Grissenda, try the build out! It is boring though, I must admit, but effective.