On 4/19 you get the Zio spell if you fuse anything with a Magician arcana (fusion forecast), so it's easier to get Garu+Agi+Resist Physical as 3 of the 4 abilities, since you get Zio no matter what for using Pixie in the fuse. It's totally possible to get those 4 abilities anytime, but it may take a really long time to get those exact 4 abilities. If Resist Physical doesn't matter, then with some time you can still get Garu+Agi+Zio on her normally. Once she learns Null Wind naturally, she won't have any weaknesses which makes her even better.
Of course, a 4-elemental Black Frost is very good, too, but that's later on in the game. After a couple of plays, I got tired of keeping track for any new playthroughs, so I just typed out what the Fusion Forecast was for every day from about halfway through the game until the end, then did the first half as I played through on that new game. It may seem annoying to always check 2 days at a time, but some of the stuff you can get throughout the game can really help out.