appropriate

Well, she can fly anyway.

_cf said:
appropriate

Wikipedia says:
The Fool is the spirit in search of experience. He represents the mystical cleverness bereft of reason within us, the childlike ability to tune into the inner workings of the world. The sun shining behind him represents the divine nature of the Fool's wisdom and exuberance, holy madness or 'crazy wisdom'. On his back are all the possessions he might need. In his hand there is a flower, showing his appreciation of beauty. He is frequently accompanied by a dog, sometimes seen as his animal desires, sometimes as the call of the "real world", nipping at his heels and distracting him. He is seemingly unconcerned that he is standing on a precipice, apparently about to step off. One of the keys to the card is the paradigm of the precipice, Zero and the sometimes represented oblivious Fool's near-step into the oblivion (The Void) of the jaws of a crocodile, for example, are all mutually informing polysemy within evocations of the iconography of The Fool. The staff is the offset and complement to the void and this in many traditions represents wisdom and renunciation, e.g. 'danda' (Sanskrit) of a Sanyassin, 'danda' (Sanskrit) is also a punctuation mark with the function analogous to a 'full-stop' which is appropriately termed a period in American English. The Fool is both the beginning and the end, neither and otherwise, betwixt and between, liminal.

The number 0 is a perfect significator for the Fool, as it can become anything when he reaches his destination as in the sense of 'joker's wild'. Zero plus anything equals the same thing. Zero times anything equals zero.[6] Zero is nothing, a lack of hard substance, and as such it may reflect a non-issue or lack of cohesiveness for the subject at hand.

People tend to get caught up in the name, but really, anyone from PC-98 Reimu (representing potential for growth), Yukari (representing the liminality and potential to change to anything), or even Satori (transient and situational power) are better matches for The Fool than Cirno, unless you are specifically going for Ex-Cirno as The World or something else to justify why you are using Cirno as the symbol for untapped potential.

Touhou Faeries as a whole embody the "childlike ability to tune into the inner workings of the world" principle, with their child forms and elemental powers.

Cirno is this, and at least as of PoFV is also tethering on the edge of something dangerous even for her (the Enma says that if she continues to cause trouble like that she can stop being a faerie), which is something that manages to make even Cirno go introspective for... uh... minutes, before she's back to her usual self.

Finally, everybody calls her a fool. I think she makes a good 0 Arcana.

EDIT: Finally, here's my 1.5 year old thoughts about a Gensokyo Tarot. This was before Ten Desires, and if I had to make a deck today, Miko would be the Emperor.

Technically, the tarot describes a pilgrimage, with the Fool being the main character. When speaking about Touhou, that would obviously be Reimu (who does possess infinite possibilities but is also quite naive and immature at times), supported by the fact that the Fool's (best) friend is the Magician which works very well with Marisa (who also corresponds to the trust and power values as well as deceit and manipulation of the Magician card).