Not too bad
At some parts I can just picture that instrument being replaced with AppleJack's voice for those parts hilariously. Like how you added in her voice as well to make it even better. Sounds like the latter part would make for a nice boss battle or character theme as well so that is not too awful bad.
The guitar was great here I think since it sounded pretty awesome. The drums sound pumped and very well done as well so nicely done going in there with the though of giving her a theme in mind. The synth sounds very cheery and pretty casual.
Really enjoyed the pumped up drum sounds as well. The bass line sounded incredibly bouncy and quite well done as well so I like it a lot too.
Overall, not too bad for a first ever. If I had to suggest how to improve it I guess I would say replacing the guitar for a banjo would be good to give it more of a southern styled feeling.