I’m in a similar situation as your friend and 2 uni friends frequently insist on paying for coffee and lunch when we meet and slip me some money for Ds each time despite my insistence. Sometimes it does feel very hard to accept but they insist. I know it’s hard for them too as we trained together and now they are doing great in their careers getting promotions I had to drop out and I’m working a few levels below and on a low income. I know it comes from a good place and they too are unsure how to support, I don’t like people taking pity on me though.
So understand what it’s like for both you and your friend.
I wouldn’t do any anonymous charity things. Or a supermarket voucher.
I would probably put together a large hamper with things she wouldn’t usually be able to afford like ‘nice’ coffee, tea, herbal teas, hot choc, soft drinks, non chilled juices, her favourite tipple, biscuits, crackers, puddings and custard, chocolate, sweets, Jams and chutneys, fancy pasta and sauces, snacks like crisps/nuts/breadsticks/jar antipasti/snack bars, nicer cereals or American ones for her Dd (b&m sell them), herbs and seasonings to make bland meals taste better, oils and vinegars, wild rice/quinoa/cous cous etc. plus you could add fancy toiletries and soap, nicer razors with extra blades, period pants or moon cups, favourite make up or nail varnish items if you know and a new pair of pjs or slippers each. Even add books if you know what she would like.
then give it in the next couple of weeks as an ‘early Christmas gift’ to use throughout the festive season instead of just after Christmas, with a handwritten card saying how much you value her friendship, positive words about her and Dd.
Then it doesn’t feel demoralising that you are paying for her food, but you will certainly make things a little bit easier for her and Dd, and with luxury treats she may not be accustomed to right now or wouldn’t buy even if she hard a supermarket voucher to make it stretch. It is an actual gift and easier to accept and reduces the amount she would have to spend herself.
Or gift a few months of hello fresh etc as she has more time to cook now.
also think planning a trip out like theatre/concert and dinner and saying dh etc doesn’t want to come could she please come (and saying you asked her before other friends) like she is doing you a favour and you’ll take care of everything might help.