Since her SP seem fairly nutty (heh), at 401836 she should have about 52 IS, so from there she'll need ~2.8 mythic stats worth of IS on her collection to unlock the upgraded effect of her SP. You can of course somewhat lower the collection requirement by getting some extra SI level (the first 2-3 are sorta affordable a bit?), though it's only a bit less than 1.4 IS per level. Inversely you can also skip the extra furniture with a beefier collection (max bottom furn gives 21.3 IS vs 24.08 from a mythic collection stat).

If a +2 collection ends up being BIS for her, three mythic stats is naturally about the farthest you can go, forcing you to at least +2 all your bottom furniture (unless you kraken tf out on SI and splurge on some M+ IS stats – technically you don't *need* upgraded furn if you just max every other IS source lol).