I've had some experience with themed drum sets like the Minnie Mouse one you're considering. Generally, these sets are designed more as toys rather than serious musical instruments. They're bright and colorful, which definitely appeals to kids, and will likely catch your niece's attention since she's a fan of Minnie Mouse.
But if you're concerned about durability, they can hold up reasonably well under normal play. However, because they're made of plastic and other lightweight materials, they might not withstand too much rough play, especially if she's very energetic.
In terms of sound, these sets usually offer a basic introduction to rhythm and drumming, but they're not designed to produce high-quality sound. They can, however, be a fun way for a beginner to engage with music, stimulate interest, and enjoy some creative play.
If you're looking for something that's slightly more robust and better sounding, you might want to consider a junior drum set that's purposefully designed as an entry-level instrument. These often come with smaller-sized drums that resemble full sets and offer a somewhat better tonal quality.
That said, if her love for Minnie Mouse and just making a start with music is the priority, the themed set might be just the ticket for bringing a smile to her face on her birthday.