It seems the tokenization algorithm used in Duolingo considers apostrophes as separators.
I've noticed they do that with other contractions too. Maybe it's supposed to be an added level of difficulty?
That's really a difference of particles. ~는/은 is used for the topic. ~가/이 is used for the subject of the topic. In this sentence, you do not need a topic because it's so simple.
When you want to talk about your thoughts on something, you can use both. (I think) this food is really expensive -> 저는 (topic = according to me) 이 음식이 (subject = this food) 진짜 비싸요.
If you want to see 저는 and 제가 together (which would be a harder sentence), you'd have to talk about yourself. 저는 제가 그 남자보다 더 강한 것 같아요 -> It seems to me that I'm stronger than that guy.
You also want to watch how you use 아주머니. It can come off insulting bc you are stating a woman is older than she may actually be. If you want to be respectful, you can stick without saying it or using the honorific question ending.