WWYD: help me get a backbone

[BasilDiffuser]

Long time lurker here! Needing advice.
Me and DH are average earners. We have one DD in nursery 3 days a week and a mortgage. For background information.
My youngest sister is turning 21 in May. In March she is going on a holiday of a life time which her boyfriend paid for the flights. He also has family there who they are staying with for part of the trip. Just a side note I would never be able to afford to go.
I asked my sister what she wanted for her 21st birthday money. Did she want spending money? She told me no she had £3000 and would rather have English money on her return.
I didn’t think of it again till I went round my mum’s house for dinner and she asked how much I was giving DS for her trip. I explained I was saving her birthday money for when she came home. Mum called me tight and said my other siblings, herself, my dad (separated) and my grandparents were all giving her some money as a surprise just before DS leaves as well as a birthday present.
I was really upset by this and said she would talk to DH about it. Since then she’s text me twice about the holiday money AND sent me a link to a present DS would like for her 21st. I feel stuck. I don’t want to look like the only tight one but can’t afford to spend the money twice!

[Bananasandchocolatecustard]

You don’t have to give her money. She is an independent person. Give her a birthday present. If others want to give both that’s up to them.

[CoraPirbright]

Didn’t you tell your mum that you specifically asked your dsis what she wanted and that this is what she asked for? Your mum sounds absolutely horrible - fancy calling one of your own children ‘tight’!

[KidCaneGoat]

It’s not really anything to do with your mum. You spoke to your sister, as adults do, and arranged it.

[mbosnz]

How rude of your mother. She can wind her neck right bloody in.

You give according to what you want to do, and what you are able to do. It's no business of your mother.

You might want to reconfirm with your sister what you're doing. Your sister sounds like she is rather more sensible, and sensitive to your circumstances (and her own in comparison) than your mother is!