Your husbandry definitely sounds good- my guess is that she’s eating the isopods. Is she defecating normally? Any signs of regurgitation of any prey? It would look munched and gooey, but chitinous shell probably still intact.
In terms of the best diet for leopard geckos, black soldier fly larvae (BSFL- also sold as ‘calcium worms’ and ‘phoenix worms’) are the best. However, some geckos find them unpalatable & require a diligent effort to get them switched over. Since she’s a baby & new to you, I wouldn’t stress too much if she does not readily accept them- you can work on swapping her out later.
Another good prey item would be silkworms (on the small side for her) or hornworms (very very small hornworms only). Chow-fed is more nutritious than when fed from leaves alone. I get most of my feeder insects from Mulberry Farms.
Sometimes some geckos won’t eat mealworms because they don’t move much. Perhaps, in her new environment, the cues that she’d normally get (like a sound of rustling or a smell or something) that prey was present are somehow being impacted.
Crickets are great for stimulating prey drive, but I have seen them eat into the body cavity of a sleeping gecko, so make sure there aren’t any left in her tank after she’s eaten. Another option that might help stimulate her prey drive would be very very small dubia roaches (as in brand new nymphs), but that might be tougher to handle for a first-time leo owner, as they can cause allergic reactions in humans who work with them over time, so protective equipment should be used.
For crickets or dubia, I’d use Repashy Superload or Mazuri High-Calcium Gutload for the amount of time indicated on the label (I always get it wrong, with regards to which species need 12 hours versus 24 versus 48). Before that, make sure they are fed a non-gutloading diet designed for insect health & maintenance. I like RoachWorld’s diet, as well as Bad Ass Bugs’ Roach diets (mine like the berry one better than the honey one) for maintenance.
Make sure you never feed your gecko with any feeders that might have ingested moldy food- it can kill geckos, especially babies.