New(ish) ball python still not eating...

[Bogertophis]

I wouldn't change to live prey if she's been raised on f/t, unless you have good reason to suspect the seller just told you that to make a sale. (I HOPE not!)

I think the problem may be in your "presentation" of the mouse to her: snakes rely on instincts, & in the wild, rodents do NOT "volunteer" to be eaten. They don't approach the snake, & if they do, it's apt to freak the snake out, as you seem to have described.

BPs are "ambush-predators"- they watch from a safe place (like their hides) until clueless prey wanders near enough for them to pounce & "get the drop on them" (ie. taking them by surprise gives the snake an advantage, to avoid getting injured along with the mouse). So when your zombie mice act "aggressive" (approach the snake) it scares them into refusing.

Feeding some snakes (like BPs) on f/t takes some little skills on your part: best time to offer food is at night, & when the snake is peeking out of their hide.

Then, using tongs, give a slight wiggle to the prey but never approach the snake with it. Make it appear to walk by the snake near enough to be noticed but out of reach- see how the snake reacts. You want to see them flicking their tongue with interest, & you want the snake to give a slight "pursuit"- that indicates they feel they're "in charge".

Make SURE the rodent has a heat signature that tells the snake it's alive- many BPs don't recognize prey that has cooled off- many here thaw the rodents, then briefly use a blow-dryer to warm them- especially the head where you want the snake to grab. This is just for BPs- because they use their heat-sensing pits when stalking prey. Many snakes don't have them- my colubrids don't, & they're much easier to feed- their prey doesn't need to be warm, just thawed, & they tend to use their sense of smell more than BPs do.

BPs tend to prefer warm prey- BUT don't thaw in warm or hot water, as that promotes actual spoilage, & many snakes will also reject spoiled prey. (I thaw in cool water only, & then if feeding a BP, briefly warm the prey & offer quickly while it's still warm. My spotted python has heat pits, but even she never cares if prey is warmed. BPs can be fussy about this. They force their owners to "get it right".

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And it bears repeating- IF you've been handling her at all, STOP. Snakes need time to settle in- no handling until they've fed at least 3+ times. Handling causes them stress instinctively (the only thing that normally picks up a snake in the wild is a predator about to EAT them!). Eating is "job #1". Handling can kill their appetite.

Make sure the snake's home has enough privacy too- in a quiet room/location, not being threatened by other pets (or humans, lol), with correct temperatures in the enclosure & several "hides" of the right size for the snake to feel "snug" & safe.

I'm reasonably sure you don't need a vet- they're great for medical/surgical issues, but this sounds like a "husbandry" issue to me. That's "what we do here"-