39.5 is small. If she's 1.5 months old and has only eaten a pinky, then that would be the cause, pinkys are way too small, and a lot of snakes wont take food if they're not the appropriate size. Reason being is I feed my anaconda adult mice, and I was trying to work out a feeding schedule with my rufous beaked snake, and he wouldn't eat his pinkys, well he ate all but one, and so instead of throwing it away(was f/t), I tried to feed it to my anaconda, and she just looked at me like I was stupid. Try something bigger, and she should take it.