The "Un" is referring to the word "regalo" (masculine), the word "hija" does not affect the word "regalo" at all.
In Spanish the definite or indefinite article modifys the noun not the receiver.
In most cases, por Is used before a period of time and para in most cases is for everything else and saying in order to.
In most cases
The female voice says "misha" or "mi isha". I'm not an expert but pretty sure hija isn't pronounced isha
You might be confused because the accent of the voice has a certain sound, but it's definitely not saying "isha."
The way the say mi hija is absurd the mi and hija shouldn't sound so separated.
It isn't perfect, it's an automated voice generator, not an actual person. Mi hija is perfectly fine, however- most native speakers say "mija," but "mi hija" with the separation doesn't change the meaning.
You shouldn't be advertising yourself or social media, this is Duolingo. I'm also assuming that you're under 13, in which case you definitely shouldn't be sharing any information- it's illegal for people under 13 to even have an account. Also, don't share email addresses. That's just stupid.