It's pretty impossible to tell unless you catch ovulation as it is happening or have an ultrasound machine to check on follicle development. We've absolutely missed it a few times. In cases where we've missed it, an indicator is shed timing. If a female who typically sheds every 2-3 months is looking large and has two sheds with only a month in between, that is a good indication of imminent eggs. Pre-ovulation shed and prelay shed occur approximately a month apart, although we have had females skip pre-ovulation sheds.

Behaviour is an important clue as well. I would assume she has not ovulated because she is still cooling. Females who have ovulated will favour the warmer side of their enclosure and tend not to stretch out.

Some snakes also glow before ovulating. Which is to say their colours brighten up, especially around the head. We have one female who looks like an entirely different snake when in this phase (we assume because she is het for Hypo).

Honestly though, it is really something you will learn with time and experience. Is your incubator ready? If it isn't, I would recommend getting it set up and tested asap!