How do I tell really kind and caring girl I’m no longer interested..?

I know I will get shit for this, but maybe someone will give me some hints too..

I’m 24, she 23 and we got to know each other thanks to our friends.
We started texting and from the start she was extremly nice and kind to me.
When we met each other irl it turned out she was like that too in person, we had a good talk and it was fun and even tho she came to my house two times (I live alone) it remained platonic. She claims to have no experience and it seems to be true, she doesn’t give me any hints if she wants anything so I don’t force anything onto her yet.

Recently I was in hospital and currently unable to move out home cause I had an operation, so we contacted each other texting and lately talking through a phone too.
The thing is.. I don’t find her attractive in terms of appearance in any way. Its not like her body is 100% unattractive, but her style of clothing and lack of any makeup.. Really don’t help.
I knew girls that had worse figure and face, but they wore clothes and makeup that fit them and made me attracted to them.

And I had feeling that maybe I shouldn’t continue it when I didn’t found her attractive, but when I got hospitalized and we didn’t see each other I kinda forgot about it and we started to know each other better through the phone and it went great until just now, she send me a photo of her face and I just.. No.. I don’t want to call her ugly, but that how it looks like.. I don’t want to be in relationship with someone that I don’t feel any attraction towards or at least I would like to not feel bad when I look at my gf face, I would rather be alone at that point.

I need to back pedal from it. But I don’t know how to respectfully tell her that its not going to go anywhere..
But its kinda hard. With other girl you just slowly stopped texting or show less interest and that’s it, but it’s diffrent here.
She’s the one that texts first and everything. Yesterday we had talk about her psychological problems and how she deals with them.

It kinda breaks my heart that I have to somehow end this, but I don’t really know how to do it.
I think the longer it goes the harder it will become to tell her.
Help.