To solve this problem using unit rates, we first need to determine how many pages Mona writes per hour based on her initial writing record.
Mona wrote a total of 9 pages over 3 hours. We can find the unit rate (pages per hour) by dividing the total pages by the total hours:
\[ \text{Pages per hour} = \frac{9 \text{ pages}}{3 \text{ hours}} = 3 \text{ pages per hour} \]
Now that we know Mona writes at a rate of 3 pages per hour, we can calculate how many pages she will write over the next 12 hours:
\[ \text{Pages in 12 hours} = 3 \text{ pages per hour} \times 12 \text{ hours} = 36 \text{ pages} \]
Finally, we need to find the total number of pages Mona will have written after this week. We add the pages she wrote initially (9 pages) to those she wrote in the 12 hours:
\[ \text{Total pages} = 9 \text{ pages} + 36 \text{ pages} = 45 \text{ pages} \]
Therefore, the total number of pages Mona will have written in total is:
\[ \boxed{45} \text{ pages} \]