Sibling issues

Good morning,
I‘be been homeschooling my two daughters who are almost 3 years apart. My older one has a learning disability so she struggles with reading, spelling and math.
Since they are practically on the same level of knowledge when it comes to History, social studies etc we do these subjects together. It also helps us save time.
The issue here is that the younger child is able to write notes, draw pictures, understand new concepts “better” and quicker than the older sibling. Although I try my best to rarely ever praise my younger daughter ( so that there is no jealousy) the older sibling is very well aware of her sister’s capabilities vs her own and gets very upset and annoyed that she is not able to draw or spell well etc. This causes her to quit learning or doing what she’s supposed to do, lash back by saying mean things to her sister or just start acting up toward me. it usually comes out with no warning at all and seems like it’s all of the sudden. We get surprised by this behavior change, but then I notice and realize the notes taken and pictures drawn by both.
I’ve also had a meeting with my older daughter and she said “it’s not fair that she knows more than me but I’m older than her”.
I’m not sure how to help my older daughter not give up on learning or continue to compare herself to her sister.
Her sister does sometimes want to correct her spelling or check the word she’s reading for errors even while playing games. And this makes her come off as arrogant and I’ve mentioned that to her before.
But these continue to happen and I’m not sure what to do .
I appreciate your advice on this
Thank you