collius, your daughter knows your granddaughter best, so I'd leave her to decide what to do.
If you're in the UK, though, with half term this coming week and/or the following week, it would seem to make sense to plan a return after the break.
A sick note should suffice to explain the absence.
Your daughter needs to present as calm and confident, though, or she will just add to her daughter's anxieties. She would be wise to keep her worries about catching Covid to herself. It won't be going away any time soon!
What is a reasonable minimum spend for an online grocery delivery??