For detail: Sharpened Snare Cuirass is a medium armor 14 ac, full dex bonus, no penalty to tealth adenemies have disadvantage on spells or abilities that cause restrained. This includes Flesh to Stone and Flesh to Gold. Portent dice are available to divination mages, and stacked with halfling luck the only enemies you can't restrain and permanently turn to stone are those with "Immutable Form", which only includes bosses like Myrkul, etc. Then just stack spell save dc items as per normal on a mage.

I just spam reckless attacks and eventually kill her, she get some damage even with this bs stacks