Gymnastics training can’t be rushed, especially in that time frame. It’s also likely that the coaches already know who they want to move up, so they arbitrarily created a new rule to effectively remove your daughter (and others like her) from the pool of candidates. If the coaches were really interested in creating a fair and objective system for graduating students to the next level, they would have defined the requirements at the beginning of the season and designed a training curriculum around those requirements. Considering that the cast handstand requirement was added on such short notice and your daughter does not currently have a cast handstand, whatever your daughter shows them in 2 months will likely not be “good enough.” I’m using scare quotes here because the coaches will probably find something wrong with the cast handstand that they can use as evidence against your daughter’s candidacy.
Ok, with that aside, your daughter is still going to need to learn a cast handstand eventually. Can she do a press handstand? Can she do a press handstand on a floor bar? Can she jump to straddle up handstand from her knees on a floor bar? These are all drills that can be safely done at home if she wants to do some extra credit conditioning. You don’t necessarily need a floor bar, but it’s a nice tool for getting used to the hand placement of a cast handstand.