Dear Daniel,
How are you? Have you already finished your exams? You have been studying a lot these days! Now you deserve a nice holiday.
I'm looking forward to leaving to spain with you and Ryan.
My friend Lucy would like to join us, do you agree? She's pretty, I think you'll enjoy her.
In these days I have been working in a pub for earn a bit of money for our trip, but now my grandmother is ill, so I have to go to her home with my parents. She lives in Ireland, I'm going to stay there only a week, so I'll return in time to leave with you.
You can write me on my mobile phone while I'm there.
See you soon!
Anna

Questo è un po' al di là dello scopo di Hi Native. Potresti provare lang-8.com.
Hai fatto molto bene. Quello che hai scritto è quasi perfetto, tuttavia ho alcune correzioni. Have you already finished vuol dire che sai Daniel ha finito, ma sei sorpresa. Se non sai, dici have you finished yet.
looking forward to leaving for Spain...
...do you agree... significa "sei d'accordo che Lucy vuole andare con noi". Se chiedi a Daniel se lui vuole che Lucy vi accompagni allora "is this alright/OK?" è meglio. She's pretty; I think you'll like her. Qui enjoy possa significare qualcosa di sessuale.
Lately I've been working in a pub to earn a bit of money...

She lives in Ireland; I'm going to...
(semicolon instead of a comma here)