Noctis has "Healing" in his profile precisely because it carries with it several items in his standard equipment, either for healing, petrification, confusion, frog curse, etc
It will not be 99, but it carries with it, and it does not need many since he use will have knowledge of the technique and is not a stupid to fall into it 10, 20 or 30 times. "Petrification" in FFXV it's not a great deal, you can find spells against it in normal stores, even normal hunters have. It's like Naruto and those ninja having kunais, shurikens, food pills. It's standard for them
BFR can be used since Noctis is covered by his summons, he does not fight alone
Glacian can cast the Diamond Dust to slow down Ashera, or even freeze her, her ice could stop and decimate Ifrit, a 1 Exaton Fire God ,Bahamut can deal with her movements to give Noctis the time he needs to cast his BFR, ANY of the Astrals can
How can she hurt him ? She is a VERY low High 6-A, and Noctis can heal himself from petrification.