Strengths:
The first verse really sets the stage well for me. And the chorus steps in and tells me what the song is about.
I'm obsessive about following rules UNLESS there is a reason to break them, so I notice how it starts with a solid rhyme scheme in the first verse, which kind of trips and falls in the second verse. Now, if you're intention is to set a solid and stable stage with the first verse and then have it get wobbly and in danger of falling in the second verse, this would be the perfect technique. And it does look like that's what happens here. We're all happy and playing at hte beach in the first verse, but the second verse points out that "her life was derailed", so that introduces some unstability. So it works for me.
Weaknesses:
That same obsession gets me with grammar, so the line "for my sister, Chris and I" is jarring for me, since correct grammar would be "for my sister, Chris and me". I, personally, would find a way to make it work and be grammatically correct, but I know that isn't as important to some people as it is to me. Which is okay.
One line feels particularly weak to me: "Her time on this earth well spent." I think there's a much stronger line out there somewhere for that spot, but unfortunately, I don't know what it is, so...
These are just my opinions, of course, so don't give them a thought unless you agree with them.
Vicki