I would definitely ask your sister what she is most interested in from a photography perspective, before looking at portfolios.
My wife and I went through this exercise before choosing our photographer. We asked the following questions:
- What photo are we going to print to share and remember our day with?
- What photos might friends and family be interested in?
- What photos have we seen that we don't like?
- We decided that we needed to own 100% of the copyright, and would do our own printing.
When it came down to #1, we decided that formals were the most important for us. We figured we'd never print and hang a ceremony picture, but instead one of our formal shots.
For #2 we figured photos of the bridge & groom with each extended family unit would be appreciated, but further, we realized it would be a great opportunity for some relatives to find family photos.
#3 we determined that the current craze of shooting into the sun would be a fad and not stand the test of time. We prefer sharp photos, vs photos that have their contrast and detail crushed by shooting into the sun.
These three answers led us to judge portfolios, and ultimately photographers by how good they were at posing people in formals. You could be the best event photographer, and ceremony photographer in the world, but if you couldn't pose people for formals, you weren't the photographer for us.
We also looked for photographers who's style most closely matched ours. I.e. some shots into the light were acceptable, but if 50-75% + of a portfolio was shot into the sun, we vetoed the photographer. We focused on photographers with great formal shots. We also splurged on a second photographer to help get the family photos done.
Post processing was another area we paid attention to, if you vignetted every photo, and/or took the clarity slider "to 11" so to speak, it wasn't an immediate no, but I made sure to ask if the photographer would mind if I asked for the RAWs of my favorite shots.
One thing we learned was that once you cross a certain point, for us in Alberta it was $2k, pricing no longer reflected portfolio quality. It was clear that those under $2k were at a lower level, but those over $2k while all good were all over the map in terms of portfolio quality to investment ratio. There were some for $4,500 that I felt both technically, and artistically couldn't compete with our photographer at $2,700.
A last comment: We did our photos with myself, my wife, bridal party, and our immediate families before our 3 pm ceremony, and scheduled 2.5 hours for them. It was a fantastic idea in hindsight. No one was rushed for photos, we got every single shot we wanted, and no one had to fill an awkward gap in the day where photos were happening. We did do another 45 minutes of shooting (aggregate) throughout the reception where we nailed down some extended family shots. Sure it ruined the "surprise moment" when I saw my wife in the ceremony, but we both felt it was more special when it was just the two of us who saw each other for the "first time" at our photo location. We also got to see each other before the ceremony and calm our nerves. Our wedding officiant strongly recommended that we meet before the ceremony to have a chat and calm nerves before regardless of photos.