What to do what to do

Thank you for the responses, certainly gave me a little more perspective.
When I started gifting the money I did discuss with them that this was being given because I didn’t want her to have to stress about money whilst studying.
You’re right, I must just suck it up until she graduates.

Why not tell her you have thought about the money you give her & have decided to put half of the money in a savings account & the other half is hers to do as she likes with.

Yep, all this above.

I wouldn't be very happy to find that the money wasn't being spent on necessities but, if you made no stipulation in the first place, it's too late to impose restrictions now.

Presumably, if the money was intended to help your GD for a finite period of time, while she is a student, that time will come to an end before too long.

I'd just remind her that the money will finish when she graduates, and after that use that amount for something worthwhile instead.

There should be no strings attached when giving money.
Unless she’s buying high end make up she won’t be spending £300 per month on these procedures.
Botox and fillers between 4-6 months. Nails: mine are every 3-4 weeks.
Is it that you don’t like these cosmetic procedures?

I suggest that you have a talk with your GD and tell her that you're unable to continue giving her this allowance and give an end date, perhaps in 3 months time.

Of course she's entitled to use the money you've been giving so generously as she sees fit, especially as no stipulations were made. That said at the age of 21 I would certainly expect her to realise that the money being given was never intended for the up keep of her appearance.

I'm so sorry that you're estranged from your son Suansas but what you do with your money is none of his business, and wouldn't be even if you weren't estranged.

Your GD at the age of 21 is an adult and the arrangement you have is with her, not your son. If you decide to withdraw your financial support and your son begins with a "torrent of abuse ... down the line", if I were you, the moment he starts I'd tell him to but out and then hang up.

I hope that whatever you decide doesn't make your situation with your son any worse.

How much longer is she studying for?

I understand how you feel, but if you’ve given her the money without specifying what she can spend it on, I would just bite my tongue and continue with her generous allowance.
She won’t always be a self obsessed student, and you don’t want to damage your future relationship.
I do understand how you feel though.

Well, if you’ve given her the money without any stipulations then she can spend it on whatever she wants. And you don’t know that she is spending your money on that. If you only want to give her money to help with living costs and you don’t think she needs it, have that conversation with her.

At the end of the day, it’s her appearance and she can do what she wants and it’s your money and if you’d rather take her out for dinner to catch up than give her an allowance then that’s your right as well.