Boss spawn point is just north above the arrow (top tip on the right). Note that the current map is not entirely accurate; see the talk page for more details.
This boss does not begin her patrol until you find her. She can be found down the road that leads east in the center of the island. She also shares her spawn point with Harn Coldstone. If you see Harn, Maxine will not be on the map. Zone and try again.
"Finding" Maxine does not necessarily mean that you have been able to see her, so it's possible that she has already left when you arrive at her starting point.
You can use the knowledge about the path she patrols to your advantage. Invoke her patroling route by coming into her ID range, then turn back towards Collector Gabrian. Further up the slope the path will fork; choose the right path. You'll need to fight small groups of Dark Flame Dryders and maybe one or two Drakes along your way. Once again into ID Range, Maxine will "patrol" right to the position you are waiting for her.
She will most likely cast a lot of nature rituals, such as Favorable Winds and Quickening Zephyr on her patrol throughout the island. If you have lost her, follow the spirits to save time finding her.
Maxine Coldstone uses the same graphic model as Bandit Blood Sworn, minus the visible green aura.