How to set boundaries with an autistic friend

[Poochy87]

Hi love shack , 

Just looking for some advice on a difficult situation that I find myself in regarding a friend. The friend in question is actually a sibling of a close friend that I’ve known for years. We’ve always kept in touch and used to meet up every couple of months for a coffee or lunch. We also always send birthday and Christmas cards each year. 
The friend in question has high functioning autism works full time and is very independent. 
Just before Covid her parents moved a considerable further distance away from her which I think that she found difficult. During Covid I was the person living closest to her and this changed the dynamic of our friendship. 
She started to phone and text me alot more and wanted to me more often when restrictions allowed. Initially I didn’t mind but very quickly it started to become relentless. She would bombard me with telephone calls and messages over several different social media platforms wanting to meet up 2/3 times a week. During Covid I worked in the hospital which was extremely busy and stressful. She would just assume that if I had a day off we would meet up and would ask for my days off every week and wouldn’t take no for an answer which became extremely difficult. 
Although things did ease somewhat after Covid it remains an issue where I find myself avoiding social media because I know that there’ll be tonnes of messages from her. 
I have tried several times to explain that I’m busy and don’t have the time to meet every week. I also appreciate that with her autism she finds it difficult to recognise boundaries. I’ve been thinking of speaking to my close friend her sibling about it but I’m really cautious about upsetting her because despite this she is a lovely person.