Here they are in the tank
Just from the photos, it already looks as though the betta is establishing the whole tank as her territory, and the guppies are afraid and trying to hide away by huddling in the top corner. You've already seen her chasing some, and that's a threat. She's trying to chase them out of her territory, but there's no where for them to escape to. You're very likely to wake up one morning and find dead guppies. They don't stand a chance if she decides to attack them.
Lots of places online will say it's okay to keep bettas with various other fish, but anyone can write a blog or internet article, or make youtube videos giving bad advice. It's tough to sift through the bad advice and find out what really works for the fish, and avoid the tendency to only want tiny tanks. Remember that the fish have no choice about what enclosure we trap them in, or what fish we trap them with... they'll do their best to survive whatever it is, but it doesn't mean that they're "happy" or thriving. Bigger tanks are also easier to maintain, since more water means it dilutes fish waste more than a small tank. Small tanks need more maintenance and experience to have them work long term.
Bettas are a solitary, territorial fish. They don't like other fish in their territory. Females don't tend to be as aggressive as males, but they're also solitary and very capable of killing other fish, especially fish that look a bit like another betta. The worst thing to put with a betta, is another betta. The second worst things are gourami and guppies. Those flashy tails and busy activity especially seem to trigger a bettas "drive it away" instinct, and the guppies are well aware that a bigger, more aggressive and potential threat is in the tank with them.
I agree with
@AquaBarb , Bettas are a soft water fish, guppies need harder water. Find out the hardness of the water where you are, so you can choose which fish would work better for you in the long run.
@Essjay is brilliant at helping people find out their water hardness! If it turns out to be on the softer side, I'd return the guppies and keep the betta, so long as you're content to keep her as an only fish. If the water is harder, and you want more of a community tank (do you want to get more fish for the tank at any point?) then i'd return the betta and upgrade the tank size for the guppies, and decide what other fish you'd like to have, and what size tank they would need, whether they could live with guppies etc.
If you have soft water, you could always keep your 5g for shrimp then
Soft water is needed for caridina shrimp, but you can have amanos and neocaridina (cherry shrimp and their colour variations) in harder water!
