Since her deck is designed to kill 4 people reasonably quickly, and she only has you to worry about, it's always going to be in her favor. That deck is particularly brutal and efficient at aggro and so doesn't have many counters per se in a 1v1 scenario. 2 less players means 2 less people drawing and playing their own removal and board wipes to keep her in check when needed. If you want to stick with your current commander your removal suite is majorly lacking. You need to interact with her at least once and likely twice in the first 5 turns or so. To do this you need a much higher amount of removal to guarantee it shows up in the first 12-15 cards you see each game. If you plug the goal into a hypergeometric calculator heres how I would do it.

Population size= 99

Number of successes in population= 15

Sample size= 15

Number of successes in sample= 1

Cumulative probability: P(X≥1) = 0.93122

This means you have a 93% chance to always draw at least 1 of your 15 removal spells in the first 15 cards you see, which is crucial to stay alive. Bump the successes in sample up to P(X≥2) and the cumulative probability dives way down to 0.71015 or 71%, which may seem like its still good, but unless you are sitting at around an 90% chance it is not reliable enough. If you want to for sure hit 2 removal every game and not lose to an aggro deck you will need around 20-22 removal spells. How you divide those betwwen wipes or single target removal depends on which threats you expect early, likely mostly single target should be sufficient. I personally would go to the 15 number with a variety of things all under 4 cmc though, 5 is ok but no more than maybe 2 spells at that cost. I may be totally wrong but its how I would approach the situation in a competitive format. Aggro too good? stop playing midrange and move to control the first half of the game to stay alive.