Perhaps the training method which led to the majority of growth she experienced while under the tutelage of her father was fending off Demonic and Hollowfied monsters in Earth's barren wastelands. It allowed Mirajane to hone her technique through real life-or-death situations, often against enemies noticeably more powerful than herself, and as such was incredibly influential. To this day Mira treats it as one of the best tools to grow and improve, hence why today she was once again standing atop the dry cracked ground she'd spent years of her life fighting in.
Unfortunately for Mira, today there did not seem to be many monsters around. While there was a beast here and there, they were mostly barely stronger than a regular human and as such were useless rabble. Mirajane sought someone, or something, strong enough to provide a good battle. After all, in order to eventually reach the heights her father had Mira would need as much training and improvement as she could possibly withstand. Hopefully her day would not be wasted here in this deserted land.