As title says, this is more of a WWYD but posting here for traffic...
My DH's BIL recently had a significant birthday. His wife (my SIL) organised a big party. She was let down quite late by the people sorting the birthday cake. My Mum makes cakes semi-professionally (i.e. she makes them properly, but doesn't advertise and takes word of mouth requests), so we offered to ask if she could help and explained that this way would be cheaper than going to a cake shop. SIL said yes please, my Mum offered to make it at cost price as a favour to relatives (although my parents and in laws don't particularly know each other well and have only met once or twice).
It then turned out that the cake needed to be huge (over 150 portions) and so more of a 3 tiered wedding cake size. Mum priced it as £120 (the cost of materials, icing, cake boards etc), DH and
I offered to pay £50 towards the cost. This is much more than we'd normally spend on a present but we figured that it was a significant birthday. SIL happy with this arrangement.
Mum made the cake, it took her about four days of intense, full-time work as was intricately decorated, it looked absolutely amazing, tasted great and very well received by everyone. However, at the party itself SIL kept saying 'thank you so much to you and your mum for the cake' as if the whole thing was a gift. BIL was also very grateful. Party was over a week ago and no offer of money has been made. As I didn't want my Mum to be out of pocket, we've paid her the full amount (our £50 plus another £70) and pretended it was from SIL.
But what should we do about chasing up the £70? My DH wants to have a word with his sister as he feels the arrangements were very clear and she's being a bit cheeky. I worry that this could cause a 'thing' in the family. SIL is lovely, so I think (hope!) this is a genuine oversight rather than CFery but it's all just very awkward. WWYD?