I've been trying to give my sister advice on a situation and need some input...

My sister has been friends with 3 girls since high school (10+ years). Friend #1 is married, Friends #2 and #3 have boyfriends. Spouse #1 and boyfriend #2 are both turning 30 within the next couple weeks. Friend #1 is throwing a surprise birthday for spouse #1. Friend #2 (who's boyfriend will be turning 30) emailed my sister and friend #3 suggesting they all pitch in for a gift. Her idea was $25 each for a gift card (assuming they'll do the same for her boyfriend's birthday too probably because she's usually only in it for herself). So couple #2 and couple #3 each point in $25 for the two of them while my sister puts in $25 for herself. Seems fair, right?... Yeah.... So I initially told my sister to make up some excuse to not join in on the group gift (friend #3 is catty and would probably call her out too) and just give a card. She's only casually friends with the significant others anyways (basically through the relationship). DH said she can't go to a party without a gift. Thoughts?