Refer Post # 1
1. Is it free to Spouses of UK nationals? -
Yes, the visa itself is free, but she will incur other expenses in completing the application,
2. Is it better via post or in person?
She must attend the Visa application office in person for her fingerprints to be taken, etc
3. Had some advice saying book the trip first so you can show proof in the application? (not happy doing this incase its rejected)
Do NOT book flights. It's not necessary but you can make some hotel or apartment bookings on www.Booking.com (or similar) where you do not have to pay any money at the time of booking. Simply cancel if necessary if for any reason the Visa application is rejected.
4. If application is made via post how long appox does that take?
Not applicable, book an appointment to attend the Visa application office
Refer to forum Schengen threads - for example my Postings detailing my visit to the Portuguese visa application office in Manchester which contains a lot of additional information