My mother has a severe migraine, so she's lying on her bed now.
My mom has a really bad headache, so she's in bed.
ーMy mother has a severe migraine, so she's lying on her bed now.
「母は重度の偏頭痛が起きているので今ベッドで横になっています」
to have a severe migraine で「重度の・ひどい偏頭痛がする」
to lie on one's bed で「ベッドに横になる」
ーMy mom has a really bad headache, so she's in bed.
「母はとてもひどい頭痛があるので、寝ています」
to have a really bad headache で「とてもひどい頭痛がする」
to be in bed で「休んでいる・寝ている」
ご参考まで!