April 24, 2020
A student can always submit improved test scores after an application deadline, and—in most cases—admission officials will use them in place of the lower ones IF the new scores arrive before a verdict has been issued.
For instance, if your daughter is applying via Early Action or Early Decision to colleges with notification in mid-December, then her decisions will probably be made at some point in late November or early December, and so her fate will be sealed before colleges receive her new scores later in December. If however, the notification isn't until January or thereafter, then the colleges are likely to consider the December scores.
If your daughter's current scores are below the median range at her target colleges, then I don't recommend that she apply Early unless she has a major “hook" (e.g., she is a recruited athlete, underrepresented minority student, has a truly atypical background, or is a VIP). I would also recommend that, if she does apply now, she should submit ONLY her ACT score since her ACT Composite of 19 converts to roughly 980 on the SAT ... thus better than her 850.
But do be careful about urging her to apply Early if her ACT of 19 is not in the median range and if she has none of the aforementioned hooks. Although there is no guarantee that her scores will go up in December, you don't want colleges to knock her out of the running before she's even had the chance to show them her best stuff.