Chances of getting an F-1 visa are remote. I would want you to reconsider the trip. The biggest problem here is, unless you declared to the consulate that you intended to convert from B to F status, they are likely to consider you to have misrepresented your true intention when you obtained/traveled on B visa.
1. H-4 is her personal application. All she needs to do is send a letter to USCIS stating "I hereby withdraw my application for H-4." Attach a copy of the fee receipt for H-4 application that comes from USCIS. I see no need for you spend money on legal fees, but that is your choice.
2. If nothing else works and she does get the H-4 approval, just have her step outside USA and reenter on F-1 visa and get a new I-94 from CBP at the airport.
3. Generally speaking, no.
1. No. An I-539 is used if you want to change status within USA.
2. You need to check with your school about CPT. The requirements for OPT as I recall are two full semesters on F-1.
3. No one can predict that. Sorry.
Status, authorized period of stay and unlawful presence are three VERY important concepts in US immigration laws with far reaching implications. The nuances in these concepts are so intricate that they can trip up even my fellow-lawyers. I see issues in this all the time.
Here is a brief primier to enable you to understand the basics. This is by no means an exhaustive analysis.
While it is permissible to change from one status to another from within U.S., it may not always be advisable.
Typically, when someone enters the U.S., supposedly for a short visit (e.g. B-1 or B-2) and then tries to change it to a longer term visa (F-1, L-1, H-1, etc.), USCIS often frowns upon it (and may not grant it), but the consulates invariably frown upon it. My recommendation in most of these cases is to avoid this type of change. If you have already obtained the change, it may be very difficult to procure a visa whenever you need to travel abroad.
I do not see any way around filing an F-1.