Birthday gift suggestion for friend going through a hard time.

When in doubt presence rather than presents is a useful rule of thumb.

Take her out to lunch or tea, to visit a lovely garden - as you live a distance away, the time you spend with her will mean more than any material gift.
That said, flowers after you have left will undoubtedly be appreciated.

If you happen to have an Amazon bag from when you perhaps received a gift , that could be useful as a hamper. The bags are usually bright and tied with ribbon. Would be easy to pack and fill once you arrive at your friend's.

How about treating them both to a really nice meal out, or a takeaway if that's easier?

My suggestions are for things that you would not normally get for yourself as they seem to be an indulgence. So if you have visited her at home before, do you know a favourite cafe/restaurant where you could order and pay for a meal, so that you all have a lovely meal and she does not have to cook or anything but enjoy the choice from the menu. , or pay the restaurant in advance for a lunch and write out a little voucher for her and her mother to go when they choose when they are on their own. If there is a good florist in her town, rather than use interflora or whatever go into the florist yourself and organise perhaps the simplest bouquet once a month for perhaps 6 months or whatever you feel you can afford. You pay the florist, no extras to other people and you can give ideas of the sort of flowers she likes. I love perfume and would rather have something that smelt lovely than those (to me) awful roses that have no perfume, look like buds but never open etc. Or you might not have a set time but you could pay for a bouquet to be sent for her birthday and any significant date, when you first met or some special memory of a day in the past so that she has the lovely flowers but also knows that yo have especially thought of her and chosen those days. Alternatively you might buy a silk scarf. Silk is a sensuous treat to have next to the skin and if you chose one in a lovely colour it would be lovely to wear, would last for ages and personally when I am having a bad day, to be able to chose something beautiful to wear and also have the knowledge of your close friend is a comfort when times are bad. Do you perhaps know some of her friends with cars who live in the same area? If they were the type of friends you felt happy to suggest this to, then you might ask them if they would take your friend and her mother on a trip to the seaside or to somewhere special to them that perhaps is not on a bus route, so you could offer to pay for the fuel and afternoon tea somewhere nearby, or if there was a garden open in the NGS garden scheme then they might be taken to visit that . The pleasure would be that they do not have to organise anything so no worries, just the pleasure of a ride out somewhere. I have done quite a bit of that sort of thing, so a friend waiting for a cataract op is hating not being able to drive and go where she wants at her own time rather than fit in with the buses etc so I have taken her to things she wanted to go to and also we had 4 of us another time so we shared the fuel costs and I picked them up at their own homes , took them to the coast, and we all did our own thing and met at 4pm to come home. Great success and as near to going your own way as possible.. If she has a particular hobby, say gardening, you could ask a neighbour to buy the monthly gardening magazine and put your card with it and post it through her letterbox, so that she definitely gets it, rather than trust the post, and that little card tells her you are thinking of her. Hope that these ideas are of use to you, but most of all having a little card or letter is something to hold on to on a bad day. Of course we all use emails etc but when I am awake and in a lot of pain at 3am, reading a note from a friend helps me to know I am not alone even if it feels like it. So whatever you actually do or buy for her is very nice but what really counts is that lovely knowledge that you have a friend who cares and is thinking of you. All the best.

There’s a gift site called Not Just Another Bunch of Flowers which has options for ill friends.

I think any of suggestions below but defo. not CBD oil, that is not an appropriate gift,in my opinion, for anyone. Google it if you don't know what it is. Enjoy your trip

Perhaps something that will connect her to you when times are difficult. A friend I have has been through a difficult time recently and I made her a very colourful blanket which she loves and puts across her knees. Something that is a hug which she will feel when you are not there.

I personally dread smelly things, as an Asthmatic they can really upset me,
I would much prefer a trip out. afternoon tea at a lovely National trust property and a few photos to remember it by would be lovely.

A bouquet of nice flowers and a lovely throw