I don't think you can really do anything.
The HCE limit on contributions to 401k takes effect the year AFTER you hit that number. So, for 2018 the number was $120k. If you were making that much, or more, in 2018 then you are classified as an HCE for 2019. (The 2019 number is $125k. So, the ~ in your number matters. If she's actually at $124,900, then for 2020, she can go back to contributing the max.)
I had the similar issue in that I got a raise at beg 2018 to EXACTLY the HCE number. I almost asked them to just short my paycheck by $1. They didn't. They have been allowing me to contribute the full amount HOWEVER, the IRS may run a test and make them refund me. I dunno. As I haven't had a raise since, I won't be an HCE for next year. In reading the rules, it's the AVERAGE put into 401ks by the HCEs, and I know that my company does limit HCE % contributions (my old boss told me so). It's entirely possible that my contributions alone this year will throw it out of whack.
If her work makes changes (like matching), then she can go back to putting in the full amount. She could also take a paycut to come under $125k for 2019, and would not be an HCE for 2020.