。
She has a fever and is in bed.
Literal
She [topic-は] fever [subject-が] exists-and is-sleeping.
熱がある is the standard phrase for 'have a fever' — note the が-marked 'subject' typical of ある ('exist'). Linked by te-form to 寝ている ('be in bed' — 寝る in this context typically means lying down sick rather than literally asleep).