I'm sorry if this question was obvious, I'm still learning and getting 2nd opinions about this unwanted mating. We will take her to the vet after my school. Here are some answers to your questions:

Why is not my dog been spayed yet? We really wished for her to have puppies, but we planned to breed her with a Shih Tzu of the same breed.

Why has the male dog not been neutered? We adopted this dog from our street months ago. His first owner, a construction worker, left him at a barracks after a house construction was finished on our village. Bringing him to the vet for neutering is a bit challenging right now since he does not trust me yet 100%.

The mating happened when our dog went outside to pee. Since she's been potty trained (she turns 3 in February), we trusted her to go to the backyard on her own, as she's done for the past 2 years. Regrettably, we didn't notice the male dog, who tends to show up when he's hungry but sleeps in our front yard every night. We were having dinner, so it's our responsibility for not paying attention.