She was struck _______________ by a severe flu just before her final exams.

• Strike someone down (phrasal verb): 
English Meaning - If someone is struck down, they die suddenly or start to suffer from a serious illness. 
Bangla Meaning - আক্রমণপূর্বক ধরাশায়ী করা।

Complete Sentence - She was struck down by a severe flu just before her final exams.

Example Sentence:
- It's a tragedy that these young people were struck down in their prime. 
- Many people were struck down by the sudden outbreak of the virus.
- He was struck down by a heart attack while jogging in the park.

Other options:
Strike on /upon something - হঠাৎ মনে জাগা।
Strike something up - শুরু করা। 
Strike something off - কেটে ফেলা।

Source: 
1. Cambridge Dictionary. 
2. Accessible Dictionary by Bangla Academy.