Perhaps Grandma’s to threaten about one item in the will? (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

HER (belonging to a woman = perhaps Grandma’s) + LOOM (as a verb = to threaten, as in “looming black clouds”), around I (one in Roman numerals). Something passed down through a family, possibly by a bequest in a will.