VENT
For the record, I sent a very nice and etiquette approved thank you note to my former roommate who came to my wedding and gave me a gift. However, I did it begrudgingly for two reasons:
1) Her gift was not from the registry, but it was all things that were just different brands/sizes of registry items. And there was no gift receipt. So we ended up with three pizza stones (2 of the 1 requested from the registry and a smaller one from her with no receipt) and had to return both of the kind we preferred since we couldn't return hers.
2) She still owes me over $100 from when we lived together. There were 3 of us and we each had a couple utility bills under our name. I made a lovely spreadsheet that would let each person input the bills they'd paid and it would automatically tell us who owed what to who. She never settled up on the final bills and she also never returned the refunded deposits from her utilities.
The third roommate moved abroad and I made two attempts before the wedding to ask what the ETA was for her check. But at this point it just feels weird to ask since she just spent money on a gift for us.
TBH, I would've rather gotten the money back and no gift!
/VENT