I would start with finding what is being reported as late and calling that company to try to straighten it out first. If it's not in collections yet they can remove the filing with the credit bureaus.
I had this happen to me with American Express earlier this year and they were able to straighten out directly. However, a 20 point drop is unlikely due to late payments that are sent to collections. If it was already in collections her score would have dropped by at least 100 points (mine had dropped about 170 points from ~820 to ~650 until I got it straightened out )
I would rather the credit bureau do the leg work. They're the ones holding credit agencies accountable for their reporting to them (they're only as good as what's reported), and it creates a paper trail against a company instead of said company just fixing the individual report to said agency.
When you file a dispute with the credit agency (e.g. Experian), they and the company reporting are held liable to investigate and provide results in a legally specified time line, or the credit agency is then required to remove the mark against your record. If you dispute with the issuing credit company directly, they don't have the same requirements or consequences.
Even if you're supposedly late, there's a universal 15 day grace period to account for processing delays, weekends, holidays, etc.
In any case, if you pull your full credit report, you can see exactly which company is showing payments made 30+ days, which you can then dispute.
Disputing pretty much everything on your record that reflects negatively is the first thing any "credit repair" company will do to boost your score. Even if the negative reports are correct, if the credit company can't provide proof to the credit reporting agency in a timely manner, it will be expunged.
I would need to see your credit utilization, payment history, and several other things to understand your score. Constantly utilizing 80%, even if you pay it off at the end of the month, reflects negatively vs. utilizing less than 50% and paying the minimum balance. Don't ask me to explain the logic there.
If you're utilizing in the 80-90% range, and paying off every month, apply for an increase. There's a solid chance you'll get approved. This will help reduce your % utilization report, getting you into the goldilocks zone.