Using weapons? Who needs weapons! Time for some fisticuffs to take advantage of the nifty cloud of daggers!
First, Shove, to knock prone, opposed by either her athletics or acrobatics.
(1d20+8)[27] Grok's Athletics
(1d20)[19] Vivian's opposition.
Then, Grapple.
(1d20+8)[26] Grok's Athletics
(1d20)[18] Vivian's opposition.
If Grok's roll on either is bad, use Sam's Inspiration:
(1d6)[4]
For his move(Assuming the grapple succeeds), he steps back five feet, then forwards five feet, basically forcing her to reenter the cloud of daggers on his turn, resulting in her taking
(4d4)[8] bonus slashing damage for entering it for the first time on a turn.
Also, for bonus fun, if both the shove and the grapple succeed, she can't actually stand from prone, having no move speed.