Hate to be that guy but since no one else has seen fit to do so I guess I will.

but she’d recently made a windfall of bits from some dubious investing.

I’m not sure what you were going for here but “dubious investing” usually means bad investments, rather than sketchy investments, or investments of questionable morality and/or legality.

she traipsed off of the locomotive and into the bustling metropolis.

The locomotive is what pulls the train. Unless she gave the engineer some fun for a free ride, she’d be getting off a passenger car or coach. (I think the latter’s usage is primarily for the UK and Commonwealth, while the former is US. Which one to use is whether the train Leech took was on a railway or railroad. UK uses railway, US railroad.)

Alternatively, she may have gotten off a dining car or observation car, or even a Pullman car (though this would be highly unlikely since Pullmans were both fancy/expensive and were for trips long enough to need beds).

However, if she was budgeting she’d probably not have had access to the Observation car, and even if she’d eaten on the Dining car (since multiple railroads ran these, and before, brick-and-mortar restaurants, at a loss to help entice travelers, she probably did. Seriously you could get a 4 or 5 star quality steak for, like, $20 or $25 in today’s money. ), her getting off from there wouldn’t make much sense since she’d need to get her luggage.

It was pretty uncommon for Leech to travel to Canterlot, since it was neither a cheap nor short trip, but she’d recently made a windfall of bits from some questionable investing.

That's still phrased to imply they were risky or bad investments. You need to phrase it in a way that emphasizes that these were questionable or dubious for moral or legal reasons, not that they weren't likely to make her money. "...windfall of bits from some investing that...well, the less said the better. It's been a pretty questionable affair at best, but she wasn't particularly worried about the ERS looking for her."

Probably not that since I'm a shit writer, but still, try and be vague, but give enough so that the adjective is applied to the intended part.

10967924
She invested in doge coin

This... This belongs on totem, presented to the world under a beam of golden sunlight