True, but there are cases where she could be correct using はるふくをかいます for a present continuous with future intention since Japanese has no grammatical future tense. Not here, obviously, since the English translation did not denote 'will'.
I put "I buy spring clothing" and it marked it as wrong with the correction "It buys spring clothing." This makes zero sense in regards to what I know about how context works in Japanese, so I'm going to report. Please correct me if I am wrong.
Not really, there is a form of verbs that makes it progressive. “I am buying spring clothes” would be “はるふくを買っています”. Changing verbs into this form is hard and you don’t nee to know it at the moment so don’t worry about it.