For an artist who loves to work with smooth, flowing paint that has vibrant color and has many months to finish a commission, the best choice would be oil paint.
Oil paint offers a rich, vibrant palette, allows for smooth blending, and has a long drying time, which gives the artist ample opportunity to work and refine their pieces over an extended period. While acrylic paint can also be vibrant and has a smooth application, it dries relatively quickly, which may not align with the artist's preference for a slower working time. Tempera and watercolor paints are typically less vibrant compared to oil paint and may not suit her desire for smooth, flowing applications as effectively.