The value of one soul is worth around 68g worth more that melee, ranged but not siege minions.
In theory she drops more souls for missed minions so it’s not like she needs the gold to be useful.
Pick up a gold income item and purely focus on poking and procing the gold passive.
Congrats you now have a low budget ADC that does tons of damage and doesn’t need much items to do so.
So why not just play her as a support? You could, however Senna kit isn’t the best compared to other traditional supports like tanks and enchanters.
Playing Senna as support is almost leaving your ADC on an island for the most part like Yuumi