As it is said in her page, she was a Creature with a power equivalent to a high Level 7 so she had enough power to go alone.

She could also go with Revis, Virgas and Violas if she went being divided as Ein.

We know nothing about the 60 floor. We only know she got there because it was part of the infromation given in her character page in volume 12.

Not to mention the demi spirit that inhabited floor 59 did not have any reason to attack filvis so she would just her pass lol.