I translated this as 'Megan is speaking suddenly', which really should be phrased as 'Suddenly, Megan is speaking.' Why would this be wrong? Wouldn't 'quickly' be 'yn cyflym'.
Yes, you are completely correct. Thanks for the suggestion, both of your sentences have been added now.
As an example, there are a series of short books in Welsh called 'Stori Sydyn', which loosely translates as 'A Quick Read'. This is connected with an initiative in Britain called 'Quick Reads' to encourage more people to read for pleasure: