As someone with Aphantasia (the type where everything is black and quiet in the mind) I recommend reading a lot. I learned to read and write early (age 5) and can only say practice gets you there. Visual imagery still works too. It just has to be there in real life not in your head. When I was unsure I remember writing down the versions of the word I wasn't sure about and then suddenly knowing which one is correct. In general building knowledge and intuition works for me.

I had lots of problems with spelling. Seeing a word written correctly 1000 times (reading books) didn't help at all. Handwriting also didn't work for me, but I think it's because of dysgraphia; I had to write every letter separately. I also used sound-to-letter mapping and grammatical rules, but they worked only if I stopped to think about every single word. What helped: - Watching a word written incorrectly, analysing how it looked, watching problematic elements, and thinking ugly and nasty they looked like. I was evoking negative emotions, comparing the word to something disgusting. Then I was doing something similar with the word written correctly, just comparing it to something nice and thinking how nice and beautiful it is, looking at it and thinking about beautiful flowers (I can see some flashes of images but mostly I have emotions and concepts attached to various objects). Later on, I was still writing incorrectly, but when I saw it, I had a negative feeling and knew I had to change it. After correction, the word looked nice. This was actually my best method, which I invented for myself. - My mother tongue is phonetic, so I was reading an English word out loud in a way it would sound in my mother language, repeating it and memorising the spelling that way. - Typing on a computer correctly a few times; my fingers memorise sequences and movement. I may not know how to spell a word or be able to handwrite it, and still type it alright. Playing to one's own strengths is the best way, finding what type of thinking a person has, how a person memorises things and what they like. Trying various things and checking what works may be a way to do it. I think it is important to discontinue methods which don't work when possible to avoid frustration.

Never thought of this, now I know why I am so bad at spelling when typing, will try with pen & paper now when struggling.

When in doubt, I write both spellings, with real pen and paper (doesn't work with a keyboard). The correct one usually feels right, the bad one doesn't, as in "not natural", "hesitant", "not fluid", irregular writing speed and the likes. So I guess I kinda learned the pen motion as the word spelling !?

I have complete aphantasia but have always excelled at anything involving words. How sounds and shapes make up words, how periods are ends of sentences, what paragraphs and chapters look like are things I learned when I around 5 years old and it unlocked spelling along with word meaning. I looked up anything I didn't know in a dictionary & learned more that way. I don't see words in my mind, I just know them. Maybe something similar would help? You don't say how old she is. Spelling is as much knowing pronunciation as meaning and letters.

I have aphantasia and struggle to spell certain words to this day. Practice (repetition) and memorization worked for me. I remember the letters of a word as a sequence. Learning to touch type also helped. My fingers learn the sequences of letters, even when I sometimes have trouble spelling a word when I think about it. When my wife, who has hyperphantasia, learned that I don't see words in my mind, said (in an alarmed voice): "How can you spell?" She actually sees the word letters overlaying her visual field, even when her eyes are open. I wish it were so easy for me. Reassure your daughter that lots of people have trouble spelling and that aphantasia is not a handicap, but simply a different way of experiencing the world. There are some advantages of having aphantasia: My wife is troubled by bad memories and dreams that feel as real as real-life. She says she sometimes wishes she had aphantasia too.