Good Spelling App for a 1st Grader

I think her problem might not be in consumption but construction. Does she write much as a complement to reading? I would probably steer her to a scaled-down dictionary and make her write sentences.

I know this is not the answer you want but it is my answer for you. Don't stress out about the spelling. If she asks how to spell a word, of course, help her. But if she has taken the time to create a sentence with words, praise her for writing something. The easiest way for her to not mis-spell words is to not write anything and that is not the desired outcome. Let her write using any spelling she can come up with and praise her ability to communicate. Believe me, the spelling will happen over time. She'll read and get used to the way the words should look. She and her friends will help correct each others spellings. You should support her writing.

Have her put down whatever it is that takes an app and pick up a book.

As a first grade teacher for over 20 years, I'd suggest not obsessing about spelling too much. I agree with Kee that writing is key; find reasons for her to write that are authentic and engaging to her. She can write letters to grandparents, notes to you, postcards to friends, etc. When you notice an error, ask her to see if she can find the misspelled word in the sentence. This helps her to develop a conscious awareness of how words should look. Remember that spelling is considered a "splinter skill", and should not interfere with her success in school and life. If you really want her to practice on a computer or I-phone, look for "word search" programs where you can input the words she's working on for her to look for (or have her create a word search for you to do.)

Starfall.com is great for learning reading, comprehension, and spelling. It is aimed at the elementary age just learning. I am not sure if there is an app version, but since it is web, it will work on a phone/tablet. I think a lot of it is in flash, though, so it would be any brand but Apple.