How lovely, Maywalk, congratulations and a very happy birthday to your friend.
I'm trying to remember what we bought for a relative who reached his centenary and in fact, not much at his request. He did have a big party which was lovely and we bought some of his favourite tipple.
Even if your friend is taken out by her family regularly, could you ask her daughter if you could take her out to afternoon tea if her daughter might help? There are some lovely vintage cafes serving afternoon teas which have opened recently. Tea in bone china cups and saucers, dainty sandwiches, cakes and scones.
We were treated to one recently and it was most enjoyable.
When we get older presents which are edible or able to be used are probably better than more stuff
although a photo of you together in a nice frame would be lovely.