I don't want to recommend any particular species for a ten gal to live with a betta I'm afraid, since it always poses a risk. Not going to 'come at you' about the idea of mixing other fish with betta either, I know that while it wouldn't be my choice, that a lot of people do, and sometimes it works out fine.
Not coming at you either when I suggest the following, just want to say that even leaving aside the betta issue, that there are not that many species that can happily live in a ten gallon. That's too small for a pleco, even the smaller bristlenose plecos I wouldn't put in anything less than a 20g. Not just because of their adult size and needing swimming space, but because they're poop monsters with a high bioload, which can get out of control fast in a heavily stocked 10g.
Many of the usual tetra and rasbora also need more horizontal swimming space than a 10g provides, and need to be kept in reasonably large numbers for them to feel secure. Neons/cardinals/harlequins need groups of 8-12 minimum really, and that's a lot of fish with not a lot of swimming space in a ten gal, but would be perfect in a 20 long.
There are some gorgeous nano species that you can keep in larger numbers in a smaller tank, like chili rasbora, celestial pearl danio, ember tetra, even dwarf corydoras - so they could theoretically live in a ten gallon, with a good school size - but these smaller species also all tend to be easily spooked, easily bullied, and much more vulnerable to a betta. If the betta turns on them it'll be a massacre, but even if the betta never so much as looks at them, these nano fish are very likely to be scared of the betta. They will be aware that they're living with a much larger, very territorial fish. That stress won't be good for their health, nor for displaying their natural behaviours. So while the stocking/bioload might be hypothetically okay if you add 8 pygmy corydoras to a ten gal with a medium sized centrepiece fish - in practice, the pygmies would be hiding all the time and not schooling around and chilling out in the open the way they would if they weren't with the betta.
So make sure to research whichever species you're considering carefully; check their minimum tank size on Seriously Fish as well as consider whether they'd be okay with a peaceful betta or not. Bristlenose and neons wouldn't work. If you do decide to add other fish, make sure you have a back up plan for what to do if things go wrong. A spare place to separate the betta if she starts attacking the new tankmates.