Like you, I need something concrete to give me a good handle on things, and this gave me clear picture of the value of Catherine's 10 guineas. So, for approximately 5% of what her father gave her, she could have bought a coat (cloak) or a (probably small, portable) writing desk. Sounds to me like her father was quite generous with her; a good picture of the relationship to clarify for us more of who Catherine is.