Thanks everyone for your advice.

I talked to my brother, my mom and MIL and I've decided I'm not going to the funeral. Matthew is okay in the car for 2 hours but after that it gets really bad with him crying unless I have someone with me to help keep him distracted. I plan to find out the next time SIL and my brother are in our hometown (they go pretty often) and go for a longer visit. That way I can spend some time with them and also go by and visit SIL's mom, dad and other siblings. I'd really like to just spend time with them and if they feel like it, have them tell me more about R and what she was like. I wish I had known her better.
When my dad died earlier this year, my mom said that there was so much support and people and food and then after the funeral is over, everyone leaves and you're left alone and it is a big let down. She said she appreciated the cards she got a week or two later because she could really have time to read them and it was something nice to get after a lot of the initial support died down. So I will send a card and Dh and I agreed to make a contribution to a bank account being started to help with funeral expenses (they are so expensive and her family is not real well off so this will be tough on them).
I'm still mulling over a sympathy gift. I found out her bday was in November so I want to give it to them then, so I have time. I found another site that makes something similar to the keychains, only they are suncatchers with the birthstones and crystals, so that is another option I'm thinking about since I'm not sure about going the jewelry route.
Thanks again for all your advice. And for thoughts and prayers for this family. It's a heartbreaking situation.