How long should I wait to get married after a close relative?

I have been with my girlfriend for 5 years and we are getting married in June 2010. We got engaged in April 09. My brother has been with his girlfriend for a little over a year and he proposed to his girlfriend in September 09. They want to set their date August 2010 and make it a destination wedding in Mexico. My girl feels that it is way too close to her wedding and that it will take away from her day. I don't feel that it will take away from our wedding. I do think it is inconsiderate for other reasons, like money and time off to get to mexico for us right after our wedding. I need help to understand this! Please help!