- Don't go for the close combat option. Snadhya's weak musculature and her apparent lack of weapons can be tempting, but you'll never achieve anything that way. Lots of assassins tried to cut her in half, reasoning that all they had to do was close the distance to end her. They were right. Problem is, none of them managed to close the distance. Snadhya has a team of competent bodyguards watching her back at all times, and can summon mighty rock protectors in the blink of an eye. Don't even approach her, kill her from a distance.
- If you're dedicating enough to seriously risk your life, then go for the overkill. Going to put a bomb under her carriage ? Put a bomb powerful enough to wipe out half the city. Going to shoot her ? Use poisoned bolts. With several, different poisons.
- Lots of assassins tend to think that because they're going to die (or worse) at the end of a mission, they'll automatically succeed. They're wrong. Most of the failed attempts on Snad's life were of the "Taking you with me" type, usually by people who thought they had nothing to lose because of their taint. Don't be too cocky, and always plan escape options. Your odds will be much better if can actually learn from your mistakes.
- Don't brag. The surprise effect is the best advantage you'll ever have. Don't waste it because you want your nemesis to see her death coming. She wouldn't be scared anyway, she's been through lots of heroic speeches. So stay as sneaky as you can.
- Be fast. Snadhya likes to appear accessible and exposed, but the moment your intentions will become clear, her entire available forces will start to cut you away from her and hunt you down. Which, considering she seldom gets out of friendly territory, means that you'll have an entire fortress's worth of minions trying to kill you. If you don't act fast, you'll fail.
- And finally, most important of all : plan ahead. What are Snadhya's habits ? How will you approach her ? Think of contingency plans in case you fail, because it'll very probably happen your first time, and if you don't plan for it, you won't get any other chances. Try to look up historically successful assassinations, or past, failed attempts on Snad's life. What worked ? What didn't ? Remember, you're not the first warrior to have a grudge against a powerful Val. Learn from history.
If I had to try one method. I would just set up a sniper somewhere with a view of Snadhya's balcony. Depending on the time her security would need to spot me, and how fast they could communicate and organize to send her to safety, the sniper may actually have a decent chance of taking her down.