Constantly worried about my sister

For the past 3 or 2 years, I have constantly become worried about my sister. My sister lives in London, and I live in another city. She’s 27, lives in her own flat, and is on benefits due to her past experiences. She also takes care of our grandmother. Despite her past challenges, I love her independence and her strive todo things. However, it makes me anxious. I do have her on Find My Friends to check where she is daily, it’s to ensure she’s safe and I know she’s in an area I’m familiar with (her house, grandma’s house etc). Although, I can’t help but get so anxious when I notice she’s in a far distance because I am fearful of all the things that could possibly happen. And when I message her/call her and get no reply, I’m 100% certain something bad has happened. I start panicking, getting sick and won’t settle until I’ve heard back from her. Then she’ll respond but it won’t be immediate. I understand she’s got things todo but please for my sanity, respond and don’t leave me waiting. The anxiety is too much. This has been happening for the past 3/2 years, and very often. It even happened yesterday, when I called my grandma to check how she was and asked where my sister was, my grandma said she went out for a walk, then I asked her where did she go and my grandma didn’t know. When I tell you, my anxiety was high, it was high. I immediately tracked her location down and texted her, where she told me where she was going / and what her plans are after, I was content. But it’s the fact I need a confirmation from her for me to feel okay. Another incident like this happened TODAY, because she didn’t respond to my message I sent her at 7:15pm yesterday, I quickly assumed something bad happened to her even though she was at my grandma’s house (according to Find My Friends) This continued to this afternoon, where I messaged her four times to see if she was okay, then she responded but I wasn’t sure if it was really her (oh my, can’t believe I took it this far) because of the way the message was worded, so I asked her to send me a selfie. Which she did, and I also asked her what her plans are for today, which was to go to church. In my mind, I am thinking she’s either attending the 3:00pm or 6:00pm mass so I can mentally prepare myself of the possible route she may take there & back. When I think of this, it makes me feel like a complete stalker. Like what the heck is wrong with me, why am I so obsessed about where my sister goes. Well, it’s because my sister has wondered off in the past where we (the whole family) were worried that something could of happened to her. She’s wondered the streets at night and in broad daylight when she was mentally unwell, which caused me trauma. I know she’s doing much better which makes me feel happy but because she’s also vulnerable I can’t shake the feeling that someone out there can manipulate her.
ADVICE PLEASE

Have you talked to her about this? Or even your grandma? Of course, you can't help that you're anxious, and to an extent, you may even have a valid reason to, however, it shouldn't be to the point that it's affecting you this much. Your sister is a grown woman, albeit more vulnerable, yet she's an adult nonetheless.
I think you should talk to her about this and maybe curate an arrangement where every morning, afternoon and night she just sends a text saying she's fine to put you at ease. To prevent you from worrying too much, maybe request that in cases where she won't be able to stick to this, she gives you a heads up first.